If Ubuntu configures X correctly for you, you also have a couple options. You can install Kubuntu along side it (it's just extra libraries, I think the link was around here somewhere). You can also try and locate your xorg.conf file, which contains all your X-Windows configuration information (resolution, mouse, etc), copy it to a floppy or the like, and then copy it back after Kubuntu install.

The xorg.conf file is usually hiding in your /etc/X11 directory, though it may move around depending on the distribution.

Oh, and don't think this was a blatant disregard of your "I'm not going to try Kubuntu again..." comment. Well, I guess it sort've is!