I used Windows Media Player 11 but it won't display my songs for some reason- perhaps because I have too many in one folder.
But here's a basic run down of the process that I snagged from a Web site.
Using Windows Media Player 11 as the server
Open Windows Media Player 11
From the toolbar, select Library then Media Sharing
Check "Share my media"
On the PS3 - Under Video, Photos or Music, select "Scan for media server"
Go back to the PC, and you should see a pop up showing an unknown device trying to connect.
Allow the device, and everything should work.
Using Simplecenter as the server
Download Simplecenter from http://www.simplecenter.com/
Install - If you only want the basic version, just click next when it asks you to create an account.
Select your shared media folders and let it scan.
Click next one last time.
Check your PS3 and your media server should now be visible.
Other Windows Notes
I've heard that many people are using Nero MediaHome and consider it to be the most feature-rich server
We recently tried setting up my roommate's macbook as a media server using two different products: Allegro Media Server and TwonkyMedia. We had numerous problems with both, including configuration issues, lack of functionality and just general buginess. I've been told that Elgato Eyeconnect works well, but will confirm as soon as I have time.
This is fascinating to me- once they start making cheaper white boards you can project anywhere, I'll be set. (And yes, I know about the Wii mote thing...but I mean something smaller and designed for the purpose of being a portable projector.)