Going to detail my 2 forays into the home server bit.
1. I'm running WHS on a tiny 4-bay HP ex470. Seriously, look up the stats. The thing is very, very underpowered at this point in time, but I put some 5400 (or is is 5900?) rpm 2tb drives in it and it's been running solid for YEARS. It does exactly what I want it to do. Store files for video/audio archiving and streaming. I have no problems running 2-3 video streams via wired and wireless here to my system, my htpc and/or the kids' tablets.
2. I'm slowly putting my freeNAS system together. Got a old dual-core AMD and I have 2 7200rpm 2tb drives in it. It'll be my "power" server that I mirror ALL my video/audio/programs/game backups onto. I'll be continuously adding drives to it when I can. As far as I can tell, freeNAS can be configured in all sorts of which-ways and I've barely even touched it. Oh, and it's free. I really like it.