Ive just completed installing fc5 with KDE, everything seems to be working properly except for the fact that the curser randomly buries itself in the left hand side of the screen.
There doesnt seem to be any trigger for it, but it usually happens after I maximise a window or open a menu etc.
Once its at the side of the screen it will keep on resetting itself there unless you move the mouse at about 1mm a second, strangly enough I can still move the curser using the number keys of my keyboard.
I am using a logitech mx1000 usb wireless mouse btw
I had the same problem with a previous Gnome install, but it fixed itself when I updated it with yum, didnt work with KDE though.
try with a normal mouse not with wireless mouse.maybe fc5 has no drivers for your mouse.