Not shure how this is related to mywireless, but in anycase, you basically need something with 64mb ram for the lowest level of Vista without aero effects.. I think. Actually for th every lowest level Vista look almost anything will work. So you can upgrade to Vista regardless really, but you wont get much visual imporement.
For the top range aero features, which I guesss you are going for, you just need anything with 128mb ram. But a slightly better card than a 9600 vanilla might be needed to run everythign smoothly.
Im not totally shure about this stuff, maby someone can tell you exactly..
oh, for games everything stays the same, games will run prety much the same as on XP with the same hardware. Apparently all games work fine under the new RC1, so by the final all games will be fine.