FC3 x86_64 problems

[leeward at msa.attmil.ne.jp]

I apologize if this is a repeat question, but I had a problem with
FC3/x86_64. I installed it and got through the install fine, but I got a
problem at reboot. When it kicks on X, I'm getting something wierd.
About 80% of the screen (bottome 80%) is gray, then there's a blue band
and the words Fedora in white going along the top of that then the rest
of the screen is blue & white vertical lines. Any idea what happened? I
had FC3 i386 on here before with no problems. Just in case it helps, I
got an Athlon64 3700+, 1 GB RAM, 256 MB GeForce 6600. Should I just go
back to the i386 release or backpaddle to the FC2 x86_64, or is there a
way to fix this? Thanks in advance.