just to pick up on the advice to install divx... i wouldn't both.
Just get FFDshow Lastest, then get AC3filter, then install the latest xvid. That will handle all the playback stuff... divx codec is unneeded since well, i wouldn't bother encoding and its not needed for decoding. since its mpeg4, xvid should be able to handle decoding in nandub.
I would also uninstall all codec packs apart from the encoding one that you need for gknot, if you intend to encode. other wise its more hassle than its worth.
Links to ffdshow, ac3filter and the lastest xvids can be found in the codecs sticky topic.
http://forum.dead-donkey.com/viewtopic.php?t=5640