XviD codec?

I purchased my first Mac yesterday and I was transfering some of my Windows files over to it. I have several .avi files that I believe are XviD encoded. When I tried to play one of these, quicktime came back and said that it needed to get an update from its site. I had a connection problem at the time and it was not able to download any files. Now when I try to play the files, it attempts to play them, without video and the audio is choppy. Is there a way that I can download this codec manually if there is one available? Does QuickTime Pro or the MPEG2 addon have support for additional codecs that will include XviD?

Thanks for any help!
Mark


Powerbook G4 17" 1.67GHz Mac OS X (10.4.3)