What OS(s) do I put in new htpc/media server build?

Looking for input and advice. Finally built a nice machine, gigabyte g.1 assassin mb, i7-960 cpu, 24gb ram (overkill but it was cheap enough), nvidia gtx 550 ti vid card, 5 HDDs with plan to use raid1 to mirror two 250gbs for OS(s) and Raid5 3 3TB drives for storage, 1000w psu all in a nice looking cooler master case. I'm definitely installing Win 7 ultimate, was also considering dual boot to server. I bought WHS 2011 for $50 and I can't get it to install. I took out all the raids I set up thinking they were causing the issue, but still no luck. WHS starts to install and fails during configuration. I've tried 5 times now and without fail, at 57% it says there is an error and to reinstall from the cd. It takes about an hour to reach the error phase, so obviously I'm a tad frustrated now.

I have two questions really. A- Does anyone have any idea or suggestion on what could be causing the install failure? and
B- is WHS even worth the hassle? I called MS and they were useless, I know, shocking...Now I'm thinking of giving Linux based Amahi a shot. Does anyone have any experience using Amahi in a home server environment? Or is Win 7 ultimate plenty capable of handling all my server/streaming needs?

I plan to use the htpc mostly directly connected to my a/v receiver setup in family room, but also want something that can stream easily to other rooms, and some light gaming, and as a general desktop occasionally.

TIA for any insight anyone can shed

yeah, i left only one 250gb hdd in and it still wouldn't load. The only thing I can think at this point is a bad image on disc.