Great info in this thread! (I hope the original poster is soaking all of this up).
I would like to reiterate that French grip (thumbs on top) is definitely the way to go. You will very rarely, if ever, see a professional timpanist play anything else. Also of utmost importance, as stated before, is "pulling" the sound out of the drum. It may seem a little pretentious at first, but it really makes a huge difference.
I'd also like to weigh in on the seated versus standing debate. thepope stated that sitting with make your playing "lifeless and mundane", but fail to see how he came to that conclusion. When I was in college, I only played seated, at the suggestion of my teacher. There are a couple of reasons for this. First of all, there is the issue of pitch changes, as was addressed before. Also, I believe that it is important to play with consistent technique and posture. So, if you have to play seated sometimes, you should probably play seated all of the time. I would suggest using a very tall seat, like a bar stool, so that you are almost standing. You should sit just on the edge of the seat with one foot on the floor and one foot on the stool (on a crossbar) at all times. You can use your "floor foot" to change pitches as needed. Playing in this manner, you will kind of be half-standing/half-sitting. But mostly sitting, I guess. Also, for me, when I stand at the drums they feel a little bit low. Playing seated puts them in a more comfortable playing position.
Of course, this is all just my opinion based on the way that I was taught and what I became comfortable with.
In a bit is shameless self-promotion, here is a Youtube video of me playing Murray Houliff's "Four Verses For Timpani" at my junior recital.