On my pc I have tried them all just about.
Twonky,TVersity, Java ps3 media server and windows media player to name a few.
Each one has pros and cons to stream to the ps3.
Depends on what format you rip to for video,pictures,music.
One will stream vob one will not, one will stream wmv one will not. Yada Yada Yada.
To many codecs to deal with.
The best culprit is twonky for me so far.

Some nas units like the hp have twonky installed (explicit for the hp).

Blue Man Group
There is no such thing as stupid questions. Just stupid answers