Assumming that you already have FCP(You eluded to that when you said your iBook was too slow when running it) .....
An eMac with Combo Drive (Retail: $1100) + a 512 meg Memory chip($80 or less) gives you a good low-middle level FCP machine.
If you can get an education discount, the Education-only PM G4 867 Tower ($1250) would be a good option as long as you could scrounge a display for it(decent 17"-19" CRT displays run under $150)
My recommedation would be to spring for a $1299 OBR eMac 800 with SuperDrive(DVD-R) MacConnection has had them in stock recently. Just go to their site and type in Recon & search. They typically post them in the mornings and are often gone by the afternoon. This is a pretty impressive machine for the $$$$ even when compared to a PC with the same capabilites; Decent RAM, Lotsa HD Space, Bright, Clear Display, G4/800 and the ability to Read/Play CD's & DVD's as well as make and DVD's.
Good Luck!
gozman
PS: Ask for a 512 meg Ram Chip for the Holidays. You have been good, haven't you?