I have the GS120 and the 12" iBook. The GS150 has replaced the GS120. If video editing is your primary reason for the computer, I'd get the iMac. It's got a faster processor, a DVD burner, a better video card, more RAM, and a bigger and faster disk, all of which are important for video editing. The iBook's only advantage is its portability.

You'll probably want to bump the RAM, but I wouldn't buy it from Apple. They really overcharge for RAM upgrades. Get either 512MB or 1 GB from crucial. Also you will probably want a bluetooth mouse with more than 1 button.

I would not buy FCE until you've played with iMovie. It's really fairly capable.