xrdb, as well as other files necessary for x, is in /usr/X11R6/bin, or similar X11-bin directory
Type "which xrdb" to find out where it is for certain, and make sure that's in your path as well. I don't know why it wouldn't have been in your path to begin with, though, so the problem may be something else.
If your trouble is "similar" but not exactly the same, perhaps you have a ~/.xinitrc or ~/.xsession file which needs gnome added to it.
I agree that KDE stinks....I've been using nothing but Fluxbox most of the time. Next install I do I'm gonna try to see how well it works with no KDE files installed....they just slow me down and look cheesy.