I've noticed that for a while now, many of my downloaded videos lose their audio video sync.

I stop the file, restart it and go to the part I left off at, and the sync is fine for a while.

Any ideas what causes this? its not all my files, just certain ones. Right now, it is happening with *.avi files

Generally has to do with what filters are being used to decode the files.

I'm using Kazaa Lite Codec Pack

EDIT

Is there somethign better to use?

What media player are you using? I would uninstall the codec pack and get FFDshow and you could also try it in a basic media player like Media Player Classic (I use MPC for all video files because it is a great media player in general).

If that doesn't work, try getting the specific codecs, such as Xvid and DivX (http://www.divx-digest.com/ is a good place to get MPC and the XviD codec; I use the Koepi build) and the DivX site itself has the DivX codec (just get the free basic one).

i use the ffdshow pack. no probs here. and it comes with a cool config util that lets you specify the codec to use.

I don't think of ffdshow as a "codec pack", even though technically, I suppose it is one. The main difference I think, is that ffdshow is high quality and designed to work together, while typical "codec packs" tend to be haphazardly thrown together and are best avoided.