Media centers are nice and convenient but they are far from necessary for most Home Theater setups. The only time they really become necessary is if you have a HUGE movie collection. Personally, I'd suggest putting the Media Center on the back burner until you figure out the receiver/speakers. I'd worry about room acoustics long before I'd spend a moment thinking about a media center. If you are dead set on getting one, you can look into HTPC's (Home Theater PC's) that can store your movies on a hard drive or look at the Escient Fireball system which is far from cheap but works very well.
