If you have WMP11, you have to add your music folder to your WMP library, right click something until you find the "media sharing" option, then if your PS3 is on, it'll recognize it and you can allow it to share with the PS3.
Then the WMserver icon should pop up in your music menu of the XMB.
Hm, ok well i found some other forum that said i had to go through all this shit of turning on these services and making administrator accounts and owning folders and omfg. he even said you need to do a disk check and defragment.
wtf. i tried the wmp11 stuff and didn't work. i shared, but when i went to find the object i wanted to share to, it wouldn't find it.
That person on the other forum was just suggesting things that you
could do, if you wanted. Some people say you should defragment before and after everything, but they're dorks. and chances are you are already the administrator. Also, you
don't need Media Center Edition to stream (I don't have it and I use WMP11 to stream...)
The steps I gave are exactly what you need to do, but it's strange the PS3 didn't show up.
This is probably the cause though-- on the PS3, there's an option that says "Enable Media Server" or something like that. It's either under System Settings or in the main list. It's not on by default, I don't think, so you'll have to switch it on. Then keep the PS3 on when you go to add it.
If that doesn't work, than I don't know what the problem is, but it's probably something Vista related.