There is a new 2.6.12 kernel available for download via whatever you use (yum, up2date, apt, etc).
Try installing that, then rebuilding it to your spec.
As for my custom kernel, yeh i built it long before i installed compat libs. I dont know what advice to offer on it except maybe consider creating a new config file. So many things have probably changed between fc3 and fc4, things beyond the gcc version. Without trawling thru the mailing lists its probably going to be a pain to work out what broke.