Just curious if you have considered a media extender-type device such as
D-Link DSM-520 Wireless HD Media Player. This would allow you to just run a 25ft Cat5e cable and then use HDMI.
I think your plan as it is should work, but using a media extender would reduce the cables you need to run and provide you with an interface to control your media.
As an FYI, the RAID support that is built into motherboards is not very efficient. You're going to lose part of your CPU to handle the RAID stuff. However, you've got a beast of a processor -- I assume that's the E6850 -- so I think you'll be in pretty good shape with it. Is RAID 1 really what you want though? That seems like a lot of waste to guard against device failure just for movies. If you're really that concerned, I would be tempted to go RAID-5. You could buy 4x 250GB drives and end up with 750GB of total storage. With a decent RAID card this would give you better read/write performance compared to the RAID-1 and also increased protection from data loss.