Go to: Services & Plug-ins (this is in the tree on the left)
Expand the Services & Plug-ins and you will see UPnP Server, click on that.
On the center section of the screen you will see 2 buttons, Start Server and Options. Go to Options.
Under Options, go to Receiver. Set it to Advanced. There are a series of check boxes under receiver, turn them all off except: Allow Visual Content and DLNA. Click on OK.
Click on Start Server.
This should be all you have to do on MC.
Now go to the PS3.
Go to Settings-->Network and make Media Server Connection is enabled
You can now Search for Media Servers. This is under Audio, Video, and pictures. Pick from anywhere.
With luck, MC will now show up on your PS3. Click on it and navigate to your content. You can pick it under Pictures, Audio or Video.
This all assumes both your PC and PS3 are on the network. I have both of mine connected to a wireless network.
Note: if you do not have a fast network, the videos will be choppy.
Good luck.