you should be fine with basically any game, as long as you dont run it at max quality, max resolution, max effects, etc.
I'm guessing you can play basically everything but games like FEAR, BF2, etc.
My old desktop had a Geforce 4 MX420 64mb...it was a POS....but i played Halo, Far Cry, WoW, and Guild Wars on it, and they all played fine, graphics looked good too (although not SUPERB like they do on a 6800go).
And one more thing, if you havent overclocked your x300, you might want to look into it. I've heard that when overclocked, x300's can actually do better than the mobility 9700 (don't know the validity of this though, but either way, theres not a HUGE diff between the two cards)