I've got MSI KN420. Been using it for 2 months now and so far, I haven't had any problem with it.
The only quirk I have with Nforce is that SPDIF Digital 5.1 out doesn't really work on my DTT2500. I get 5.1 sound from 5.1sound source. But if the source is 2 channel, Nforce puts it out as just that. 2 front speakers. Funny thing is, DTT2500 detects it as being DD5.1 sound source and refuses to switch it to Pro-Logic. So I'm stuck with 2 front speaker when listening to mp3, games, etc. Fair bit of discussion and complaints going on. Hopefully there'll be a new driver out to fix the problem. I think this problem exist for Asus nforce as well.
Video performance is adequate. I've been using onboard vid for about a week and so far, it'll play all the games I have and performance isn't too bad either. The fact that after I sold my old Geforce2 Ultra, I can still use the computer is a plus.
Nforce driver is pretty easy to install. Just run the setup file, and after reboot, everything worked without trouble. Ah.. might be worth mentioning...I counldn't get Nforce to work on Win98. I believe the driver support from Win98SE (or WinME) and above.
Just wondering if you are set on getting Athlon XP? Currently P4 1.6A seems to be the best value for money. You should already have a DDR ram, and I assume a vid card, so it's just matter of getting mobo and CPU. Can't be more expensive than A7N266 + XP1800+. Best of all, it's not VIA
Anyway good luck with whatever you get