I had the same problem on an "old" PII 400 box with an ATI Mobility M6 graphics card. I had to install FC1 in text mode (you can choose it right after booting from the first installation disk, before running X). After installing in text mode, I was then able to boot to X, no problem, and the card was well recognized.
"I'd crawl over an acre of 'Visual This++' and 'Integrated Development That' to get to gcc, Emacs, and gdb. Thank you."
-- Vance Petree, Virginia Power