Great Idea!
Hootie,
Just to piggyback here, I'd say go for it! I did it just before the summer I transferred schools, so my job selections in the Guard were limited to those where I could go to Basic AND Tech school over the summer and be back in time for the Fall semester to begin at my new school. I felt this was absolutely critical for me, as I could not waste any time. The age limit for UPT (26 1/2) was a factor then, but I think it has been relaxed now. In my case, I started applying for a UPT slot in my sophomore year just to get the practice and to get to know the people I would need to be impressing. I knew I did not have a chance while I was a soph or junior, because there were a bunch of guys ahead of me who were bumping the age limit. But the interview pratice was worth it, and they all knew who I was by the time I finally got accepted 3 years later

. BTW, I made it to UPT with only 6 months to spare!
As far as the job you do in the Guard, I'm not sure it really matters. Flying would be great, but realize that while in school it may make your life difficult. Those airplanes tend to leave and not come back for awhile (as in days or weeks later). I'm not an expert, but look into it. I ended up refueling airplanes out on the flight line (it was either that or be the Base Bus Driver), but as it turned out, I don't think I could have had a more ideal job while in college. At my unit, I was able to get hired full time in my field after Tech school, which was awesome because it gave me tons of down-time to study when I needed it and the pay was great. I still got to mingle with the pilots on the line, and it is a simple enough job that you will still be able to excel at it while preoccupied with school and flying. And, driving fuel trucks all over the world (ie while on deployments) was fun. It kept me outside, and near the airplanes (not just our own, but everything that flew in and out as well). The other full-time guys there ( a mix of Civil Service and mil types like me) were great and were usually willing to help me out with changing my work schedule as my school schedule demanded. My point on the job selection subject is, set yourself up to succeed. I knew MANY guys in my unit, headed in the same direction I was, who were great guys and who were Crew Chiefs or mechanics in the squadron. They were going to school full-time too, and I have to believe their jobs were much more distracting than mine was. As a result, it was harder for them to be a "star" in their field, and that's what counts. When it came time, in my third (and last) interview for a pilot slot, they hired me over them even though the other guys had way more contact with the pilots than I did. I had enough to get selected, whereas some of the guys I was competing against may have had too much, IMO.
Lastly, most Guard units get only one UPT slot per year, so it's highly competitive. I knew this going in of course, but it still looked better at the time than competing against 250 cadets in my ROTC Det for 4 pilot slots. Things obviously change, so try to get a good feel for the current conditions. They really like you to live in their state too, because believe me they have enough of the people who are just there to use them. My last piece of advice is to never give them the reason to feel you are using them in any way. Don't hide your aspirations, in fact they'll appreciate that you have them, but be careful about how you present them. I'd try to stay in your home state if at all possible.
PM me if you have any other Q's OK? And DON'T GIVE UP!! It will happen if you want it to!