Lets start of with the download Here
How to install Medica Center X on a Mac that is running OS X
Access your Multimedia files with Media Center X
U MUST EDIT THE PROGRAM SETTINGS BEFORE DOWNLOADING FILES.
For security reasons, you must specify which directories you want to allow downloading from. By default, you will only be allowed to download files from your "C:Documents and Settings" directory which includes your "My Documents", "Desktop", "My Videos", etc. folders. If you try to download from any other directory that is not specified you WILL get a Forbidden or 404 error.
To add the directory you want to download from, click the Settings button at the bottom of any of the File Server pages. You should do this on your PC as it will be a lot quicker and not on your PS3.