mouse freezing in X Windows?

[David Piniella <dpiniell@newssun.med.miami.edu>]

I'm running a woody unstable box, GUI is X-Windows with XFCE4; my mouse 
keeps freezing in x-windows. I can use the keyboard to do stuff in xfce 
(run commands, tab through options, type in an xterm, etc) and if I go 
to another console (e.g., alt-F2,)  and then go back to X-windows 
(alt-F7) I can use the mouse again...but within a minute or two it'll 
freeze again.

I've tried "nice X -a -20" to renice the X mouse process but I get an 
error that the process is already running on :0 ...I don't want to 
respawn the server...

so my questions are:
why is my mouse freezing (or how can I find out myself?)
and
can I renice a running process? if so, how?

--
David Piniella
University of Miami