You need to 'allow' sharing to the PS3 in Media Player, then it should pick up the server. You can also use TVersity, which will transcode any unsupported formats, but I used to find that a bit choppy with HD content.How do you stream from the PC? When I try it just searches for media servers for ages!
Looking into the streaming side, this seems to have some good, straightforward info Manic:
http://www.neogaf.com/forum/showthread.php?t=158357