What you chaps need is a media server called TVersity. This will decode your avi files into the relevant format that the ps3 needs to view them. I did try it using windows media server but it wouldn't play the video's. With TVersity it works always.

PM me if you get stuck, it is stright forward but at the same time difficult if you don't know what your doing.

If you just want to listen to music you only need to change the permissions on media player, then do a scan on the ps3 and up should pop your PC. You can then access your mp3's etc.

http://tversity.com/