Now, are you looking for a theater, or are you just looking for a really nice family room setup with a killer TV & surround?
If #2, then you want to think about options like how the couch/TV will be configured, what type of setup you will be using, and how the surround speakers will be placed in a specific room. After weeks of searching for a home, we finally decided to have a home built.. Well, there was only about a 10% difference between buying a 30 year old home and buying a brand new home, so it became a no brainer.
Anyway - an unfinished basement is THE place to put a true home theater. The family room offers a nice plasma or rear projection setup, but you are dealing with finished space, and open walls... just getting wires where you want/need them is going to be a process. But, it is all possible, and before you move furniture into the room, you want to run wiring, repair drywall, and paint the room.
I went with the 50" plasma with a motorized 100" screen that drops in front of it for front projection. During the day I have good viewing and a 'daily' watcher, while at night I have the killer projection setup. It works great for the family room and allows me to really get the best of both worlds. Most of all, the room is setup (typical) with the kitchen right off the family room, so we can prep dinner, wash dishes, do chores, etc., and still be in sight of the TV with no problem. The fireplace is on the rear wall, so it does not interfere with the TV. We set the TV up as the focus point.
In my last house - no fireplace = no issue. If we were going to add a fireplace it was going to be in the corner opposite the TV to not interfere with the real focal point of the room.
Fireplaces? Cripes - will someone please shoot interior designers?!?