My iMac won't finish the start up process because it stops after the "BIG in size" quicktime extinsion. I have disabled it but i think it needs it to start up. I tried installing quicktime 4 off the iMac software disc that came with it and it won't start the program.Then i tried installing it off of a cd that has it included, while under no extinsions mode, and it won't come out now.

Your Mac does not need quicktime to startup. I've never heard of the "BIG in size" quicktime extension, but trust in the fact that you don't need quicktime to startup. Look elsewhere for your extensions conflict. Try diasabling ALL quicktime related extensions in your extensions manager control panel (duplicate the current set, rename the copy, and then edit it's contents). It does seem that you have an extensions problem.