um....
1. go to the apple in the upper left hand corner
2. click it
3. go down to system preferences
4. click it
5. in the new window that pops up, click on displays
6. the window transforms into a display screen..my bet is you have it on a small resolution (800x600 or 640x480) scroll down to a lager resolution like 1024x768 or 1280 x 1024 whichever looks best
7. hold command (the key next to the spacebar) and then press Q
now you should have your screen back to normal size? (this is assuming all quicktime did was mess up your resolution)
also, when you want to open a picture, hold control and click on the file... when the box pops up, go to "open with" and choose preview or another application besides quicktime
hope this helps....if it doesnt, try to be more specific about the problem and i might be able to help you more :-\
good luck..and get a mac at home *wink* *wink* ...