As I mentioned a couple weeks ago with the initial Stargrunt playtest report, I really want to convert the units of Starcraft to the SG2 rules. Caveat the first: I only ever played SC1. Hence, SC1 material.
Terran's pretty simple and probably not terribly controversial.
Marines are standard grunts with gauss assault rifles (FP2, Imp 1d12) in d8 heavy non-powered, but environmentally sealed, armor. Move of 6", leadership and experience as for standard humans.
Firebats are effectively marines with flamethrowers; this gains them two die shifts in Close Combat and the Terror quality. Firebat armor is also fire-resistant (handy!); if using the optional Fire rules from page 58, firebats need not test to survive near fire markers (though they can still be killed in close combat by a unit with a flamer; think TF2 pyros).
Medics in SC can't shoot... this is no good in SG. I suggest giving medics a PDW or similar weapon to defend their wounded charges (FP3, Imp 1d8, can fire in close band only). In addition, medics grant a +1 to die rolls to stabilize casualties, per page 60. Armor is kind of tricky; d8 is the heaviest non-powered armor gets, there are no rules for giant shields, and having mixed armor values within a squad complicates fire resolution. I'm for giving them d8 armor and trading the defense of the shield for the offense of a weapon. Not like the shield ever did them any good anyways... If you're really concerned with being canon, go with d10 non-powered armor and no weapons, but don't say I didn't warn you.
Ghosts probably fall under the (hideously overpowered) Sniper rules on page 28 using conventional sniper rifles (FP 1d10, Imp 1d10). Their cloaking is also, conveniently, modeled by the sniper's hidden unit rules. Special ammunition is not within the scope of this post. As with all instances of the snipers rules, I recommend not using ghosts.
Stimpacks can probably be modeled by increasing FP on Marines from 2 to 3, and increasing Marine, Firebat, and Medic movement from 6" to 8". They require a reaction test to use, and, at the end of their effective duration (possibly 2 turns? One action to stim, three actions of effectiveness), casualtying about 1 in 4 of the subjects, with a possible reduction to 1 in 6 with a medic in attendance.
So that about covers infantry. Bunkers fall under the Buildings rules of page 57; probably Armor 5, with doors of Armor 2. They're pretty small, since they can only hold 4 people... Probably size 3 as far as vehicle / building stats go. Sensor scans are off-table support (page 45) that generate EW counters (page 53); the difficulty of calling in a sensor scan, and the quality of the scan, will vary by scenario. Likewise, siege tanks are off-table artillery (page 47), of large caliber (so 6" burst radius), and firing general-purpose shells (Imp 1d8 against both infantry and point targets). Battlecruisers are just orbital fire support; massive shells for 10" burst, but general purpose (d8/d8) and a longer delay on arrival because they're in orbit, and the difficulty to call them in is higher. Wraiths fall under air support, and are kind of an edge case that I'm not looking to develop presently. Don't even think about calling in nukes; to paraphrase an SPI wargame from the 80s that I once read, "To simulate the use of nuclear weapons, dowse the playing surface liberally with lighter fluid and ignite."
Dropships, however, are actually an interesting topic; SC dropships are what SG would classify as small VTOL transports. Their 8-man capacity could easily fit into a size 2 vehicle chassis, along with armor 2 and basic (1d6) ECM, and you'd still have 2 capacity points left over. Me, I'd use those two points to put a pair of door-mounted Gauss SAWs on it a la various American transport helicopters in Vietnam, but if we're really sticking to canon, we can hold off on those. Lord knows your marines need the fire support, though...
Goliaths are tricky. I've got two possible implementations in mind. The first treats them as Size 1 Vehicles with Armor 1, Speed 6", a pair of SAWs, a dedicated AA (page 49) Guided Missile/L launcher, and 1 leftover capacity point (maybe extra ammo for the missiles?). Note that this makes them kind of scary in terms of raw firepower (see below). Note also that, as in SC, the only thing they have going for them in melee is armor (and unlike in SC, vehicle armor only applies to the front; it's reduced on the sides, top, and rear. Yes, vehicles have facing.)... except that there are also no rules for engaging vehicles in melee in SG. We may have to hack those in, treating Goliaths as powered armor for purposes of odds calculations (they're big and intimidating, and Size 1 vehicles are the same size as PA), but not for melee resolution (they're kinda squishy once you knock 'em over, crack 'em open, and eat the softlings inside). Firing by Goliaths is resolved as follows: in a single action of firing, you can fire one or both SAWs at a single target, or you can fire the GMS at a single target. When firing both SAWs at a single target, you roll your quality die and 2 FP dice, one for each SAW (per errata / clarifications on multiple support weapons in a single squad). If you use both of your actions for firing, you can fire both SAWs at a target and the GMS at something, or one SAW at each of two different targets, or two SAWs separately against the same target (to suppress rather than kill), or one SAW and the GMS (though since there's no penalty for firing both SAWs, there's really no reason to only fire one). It's fairly straightforward, really, but the SAWs give it dakka on par with a squad of marines, and the GMS makes it much better at cracking tanks and other vehicles than marines would be. This makes sense, but is not strictly consistent with the numbers from SC. They'd be great for fire support if you don't want to put SAWs on your dropships, and take up 2 marines' worth of carrying capacity...
The second, simpler, implementation is as heavy slow powered armored infantry (speed 6", 1d12 armor) armed with a Gauss SAW and Multiple Rocket Launcher packs (page 31). Note that ML packs are also pretty darn scary by RAW, since they have unlimited ammo, and are excellent against infantry. They are, however, not so good against vehicles, and therefore don't fit the canon. Further, this version of the Goliath, while simpler, kicks ass in melee; another breaking away. Therefore, the vehicle conversion is probably empirically a 'better' conversion.
Vultures I don't really care about. If somebody really really wants 'em, maybe I'll stat 'em up. Expect size 1 vehicles with high speed and crap armor. The real problem is weapons; grenade machine guns are really quite scary in SG (they're like SAWs, but with an extra anti-vehicle / anti-building function), and single-shot grenade launchers are not considered. There's no good middle ground. So I'm holding off on vultures for a while yet.
And that's all for Terrans, unless I'm forgetting something important... oh, right. Don't bring SCVs. Problem solved. If you really want them for like a scenario objective, treat them as marines without guns, and probably Green experience. Also Valkyries should not be atmosphere-capable if they're anything resembling a 'space frigate'. Another problem solved. If you really want 'em, make them off-map anti-aircraft artillery and increase the air defense environment score (page 49) of one side to account for their actions.
Expect Zerg in the next couple days. I don't really intend to do Protoss for a number of reasons; they just don't interest me that much, I'd have to bend a ton of core-ish rules (Shields? Psychic powers? Wut?), and their psychology is trickier than Zerg. But the Swarm is coming to eat your marines...