I dunno about the specifics of what you do, but using my Radeon 9250 in Vista (unsupported, but a driver is provided) failed miserably... however, switching to my nVidia 5200FX gave much better results... so as far as nVidia cards go, anything above a 5200FX will be fine (though not necessarily optimal).
Networking wasn't a problem for me, though I'm on wired ethernet... my 10Mbps NIC was way too old to have a driver but to my surprise an XP driver for it worked flawlessly, though I was using Vista 32-bit and apparently the 64-bit version of Vista does not support XP drivers, even if they're XP64 compatible. I've not tested this, I don't have a 64-bit system.