So you have seen the same slowness and heavy swap usage with GNOME, KDE3, and KDE4 when running
knoppix, mandriva, and ubuntu?
Makes me think you have a hardware problem. Are there any warnings or error messages in /var/log/messages?
I am just grasping here, but I think I would try clearing the CMOS on my motherboard.
I don't know.
I don't have an answer for this either.