I'm playing as Terran against Terran AI now to try and train up for multiplayer, and I keep getting out-matched in the initial ground battle, even though I'm doing the correct build order and micro'ing my SCVs. By the time I first have up my academy, the AI is already at my expansion with 12 marines and 3 or 4 medics. Should I be losing to the AI, or do I just fail? It's one of the brood war maps, so I'm guessing the AI is scripted, but I'm wondering if it's cheating with resources and build times as well.

The Starcraft CPU can naturally micromanage better than most, if not all human players. They also don't have Fog of War, and know exactly where you are.

"CPU can naturally micromanage better than most, if not all human players. They also don't have Fog of War, and know exactly where you are.  "

I believe Starcraft AI gets to build buildings for free but still need to spend resources on units. That being said, unless you have a custom AI, you shouldn't be out-massed that badly.

Im pretty sure the No fog of War for AI is a myth, as far as I know thats just an old competitive gamers tale, the AI must have some sort of visual limitation, otherwise the AI would auto attack from outside your Line of Sight. Everytime I play an RTS I think "The AI must be able to see what Im doing" to myself but I haven't seen anything to prove it. 
 
Normally the AI can cheat in that it is given a higher handicap for resources than at lower difficultys.