All of the projector's wires (Component Video, VGA, S-Video, Composite) and my rear channels (Left Rear, Right Rear, and Center Rear) all run through the ceiling (since the room is in the basement). so there are 10 or so wires running through the ceiling, If you do this be sure to run the speaker wires separate from your video wires, because the speaker wires have a much higher power and can easily introduce distortion into your picture if the wires run alongside each other for any great length.
I got all of my wires from monoprice.com a 50ft VGA cable only ran me $18, and the other ones (all 50ft) were even cheaper then that.
The screen is about 20" away from the wall to fit all the equipment and the sub-woofer (dead center under the screen). The back wall is also painted flat black to keep any light from reflecting and taking away from the picture.
As for getting the projected image to "fit" on the screen, Most projectors have a zoom function, mine is a manual zoom, basically just a knob next to the focus around the lens where I can zoom in and out. You'll notice the sides of my screen have a 2" black strip, this is completely non-reflective and will turn any light projected on to it into a dark dark black. Ideally you'll zoom the screen such that it will spill over into this strip just slightly. this will give the image a nice SHARP edge and make it really pop.
Hardcore Home Theater enthusiasts will create adjustable top and bottom borders as well that can adjust to fit the various wide-screen formats found in Movies (most movies are WIDER then 16:9 and still letterbox even on widescreen displays). Unfortunately for me the room is too short for my projector to fill my screen, even when zoomed to it's largest it still misses the edges by a few inches. I have a few inches I could move my projector further back, though I don't know if even that would be enough.
As for those two screens you found, I'd DEFINITELY go for the CircuitCity one over the BestBuy one. If for no other reason then it has a silver/gray base as opposed to a white base. A silver/gray will be much better for movies and video games... they call theaters the "Silver Screen" because real movie theater screens are actually silver, not white
White screens are typically used for office applications...