I'm not sure if this has been posted already but:

I capture using NVidia's Personal Cinema with virtualdub using the XVID codec and i my video and audio will slowly get more and more out of sync. At the beginning it is normal, but as the captured movie progresses the audio/video will slowly become offset. After about 40 minutes the audio is about 2 seconds off.

Pentium 4 3.0GHz
512 MB Ram
Turlebeach 7.1 w/ spdif IN