I can't really give you much insight, just an observation or two.
My "home media server" is just a PC with a lot of storage space, 4 x 2TB Western Digital HDDs in Raid 5. The OS started as Ubuntu 8.04 LTS back in 2008, but there was something I wanted to run that required 10.04 or higher so I performed a fresh install with Ubuntu 10.04 LTS.
I don't really care for the Media Center type software so I just have the various shared folders auto-mount when the Home Theater PC boots (although both the Media Server and HTPC normally stay on 24/7). When I want to watch a video or listen to music I simply look through the folder to find what I want. No need for streaming software or copy/paste, I double click on the file and off we go.
One thing that I would recommend, have the OS on a separate drive. My system is actually running a software Raid that isn't bootable so I have to run a separate OS drive, but I think that I would do it anyway just in case of an OS crash or corruption, or if I should need to upgrade the OS. It doesn't have to be large or fast, currently mine is a 250 GB IDE with an accumulated run time of 8+ years.
I hope this helps, if you have any questions, ask away!