Short answer: It's too wide when you view it in QT Player because QT Player doesn't automatically make it a 4:3 width:height ratio like iMovie does. If you rescale it to 640X480 or some other 4:3 ratio size, it'll look correct. The color shift is almost certainly due to how QT Player draws the video on screen, and is probably related to it not deinterlacing the video for you. It can do this, though I'm not sure if you need QT Pro for it--it's buried somewhere in the options. Try opening the video in VLC and turning on deinterlacing.
Long Answer:
The stretched thing is as others said. A standard NTSC TV has (in theory, though there's a lot of variation that I don't clearly understand) 720 collumns by 480 rows of pixels that it draws every 29.97 seconds in two passes (that's interlacing--it draws every other horizontal row, then starts over and fills in the blanks, so you really have 60 720 by 240 images every second).
Standard DV video, which is what iMovie uses, is exactly this format--720 by 480 pixels, 30 (ok, 29.97) interlaced frames per second.
Since a standard TV has a width-to-height ratio of 4:3, the pixels aren't square--they're a little taller than they are wide. You can actually see this if you get really close to your TV screen--you'll see little vertical color stripes that make up the pixels, and they're slightly rectangular instead of square.
Computer monitors use a much simpler and more logical system; pixels are always square, and there's no interlacing--it just draws one whole frame then another.
The problem with this is when you open a 720X480 non-square pixel interlaced image in a computer player, it looks funny; it's too wide (the pixels should be horizontally "squashed" but they're not) and since your monitor refreshes MUCH faster than a TV you can actually see the interlacing lines. This is likely the problem. iMovie compensates for all of this automatically--it de-interlaces the image and forces it into the correct aspect ratio so it looks good while editing.
