I am a VMI cadet in the SMP program here. PM me if you have more specific questions but here goes...
-A few guys in the SMP program here enlisted in highschool. What they will do is "STO" aka split training option. This means you would go to basic training during the Summer and AIT (advanced individual training aka your army "job specific" training for your MOS the next Summer.
-I enlisted while I was at VMI and most of the SMP program people here at VMI did this. You will STO if you do this too.
-This is just my opinion but you could get an Army active duty contract or scholarship if you work hard at VMI and being in the National Guard means you can't take an AROTC scholarship so keep that in consideration.
-As far as RSP (recruit sustainment program) drill is concerned, you will do that from the time you enlist (swear in at MEPS which is the military entrance and processing station) until the time you finish AIT unless you get contracted to commission then you won't go to your unit or RSP you would drill with SMP.
-For example, I contracted with AROTC to commission after finishing basic training so I didn't go to AIT and went to the SMP unit drill and I have been drilling with them until I commission.
-Hope it helps and remember this is a pretty big decision, thoroughly research your options before you put your right hand up and swear to defend the Constitution and basically become government property. =)
Rah Virginia Mil