I'm just about done with my Maine Army National guard application. (hopefully the board in DC is going to be looking at my packet this coming week) I'm going to start out as a 2nd Lt in the Medical Service Corp. but I'll be in the State Medical Command. I have to drill one weekend a month and the two weeks in the summer, and I'll get the drill pay. They let you get out of drill if you have a test/rotation requirement or such. I.e. you're in medical school/residency first, national guard 2nd. (i think a lot of this depends on your commander).
You're undeployable until after residency but have to sign a 8 year agreement. I'll become a captain and move over the medical corp right after medical school graduation. Once I do finish, I'll be deployable for 120 days total (90 days boots in the sand) every year and a half. I'm not sure how exactly being deployed works - I don't think you go with full command - but that's a little ways off. Being that i'm a 2nd year, and if I do a 3 year residency. I'll be deployable once after residency. If i do more than the 8 years there are other options available, such as loan repayment ($50,000 for 3 extra years right now, but might change a little bit)... This is very quick and dirty, PM me with any questions about it.