Although this is a tversity thread, I thought I'd comment that the ps3mediaserver app (link posted earlier) works superbly for my needs.
For the longest time, I couldn't play any video file without having the video and audio stutter every 15-30 seconds. Copying files from my pc to the ps3 were taking unusually long, and this was with a quad core, raid 5, 8GB RAM, and gigabit network connections. It turns out that there is an known issue with Windows 2003 and tversity, and the developers were able to reproduce it.
However, ps3mediaserver has none of these problems and all is well. It also does real-time transcoding just like tversity so I'm completely happy with it.
Thanks for the suggestion, I would have never found it otherwise!