Problem with Graphics card for Final Cut Pro

I've just tried to open Final Cut Pro vers 4.0 on my G5 iMac, (about 2 weeks pre Intel!) Apparently, i need an AGP graphics card to run it.
My iMac has an ATI Radeon X600 XT. Do i need an older version of FCP for this mac? It's only a year old (the Mac) so find it odd that i can't run an old vers of FCP on it. Also is it very hard/ expensive to upgrade my Graphics card on my iMac? I was under the impression they aren't so easy to upgrade. I've Just found a review for Final Cut Pro 4 dated 2003!! Can my 2006 iMac REALLY not run a program as old as this??? I find that incredible!

Something you may want to look at. Final Cut Pro 4.5 HD and earlier not supported on Power Mac G5 (Late 2005) or iMac G5 (iSight).

Cheers, for that. I did do a search on the apple site but obviously didn't word it properly. Thanks again.

I happen to see this on another site. In the AGP line you need to replace that with PCI instead of deleting it.

http://screenplayer.sg/?p=100