I've just installed RH 5.9 and configured my system to start
in runlevel 5. Gdm starts correctly, but doesn't get keybord
focus so you can't login. CTR-ALT-Fn should switch to a
console, but it immediately switches back to X.
You can login to a console (without seeing it) and (for
example) do: init 3 and the X server is shut down.
If you then (of if you have booted in runlevel 3) type:
gdm appears (again) and evryting is working like my old 5.0
fixed in a later initscripts/XFree release