I am having the exact same problem. I was blaming my lock ups on the video drivers, but I just noticed that when ever I get a phone call Win2000 freezes every time. I've disabled the call waiting feature but it doesn't help. This is really weird.
System:
Celeron 400@450
Abit bx6 r2
Diamond Vipper v770 (tnt2 non ultra) Nvidia 5.4
Sblive value, liveware
ACTIONTEC PCI CALL WAITING MODEM
128meg
Maxtor 5gig