My guess is that you have final cut 4, not 5. FCP 4 will not run on an intel mac, claiming it needs an AGP graphics card. FCP 5 will actually run on an intel mac, pretty well, and I even did a 5 cam multicam with DV footage using FCP 5 under Rosetta (it was the non UB version).
Follow Marks link and investigate the crossgrade, which you need to get for it to work on your iMac.