Here's how we have our media server set up at my house (Dell Blade server w/2 Pentium Dual Cores, 8gb RAM and a 1.5TB HDD and an old 80gb hdd). It's very basic but works splendidly.
Main OS: Ubuntu Server Edition (check the options for Samba during the install).
HDD Setup: All ext4. The OS is on it's own 20gb partition on the 80gb drive with
/home being on a separate partition. The reason the main OS is on a separate drive is we were debating putting it on an SSD, but never got around to it. The 1.5 TB drive is mounted to
/media/data (make sure this is done in
/etc/fstab, not manually, as mediatomb likes to have it available when it loads).
Media Sharing: Set up samba to share
/media/Data (allow guest, no authentication sharing). Standard samba setup really. Install mediatomb (UPnP) and follow the instructions on their wiki regarding sharing with a PS3 (basically uncommenting 1 line in a config file). Use the mediatomb web interface to select which directories you want to share. Pretty easy.
Other Thoughts: Read through the mediatomb options and wiki's, there's a lot of other features you can enable through the GUI and also the config file. I know we changed the behavior it monitors directories and also how often it scans directories for new files.
It should be relatively easy to set up, and when you are done you have an excellent media server.