Mouse not reconized under Xserver

[Thierry <tchatelet@free.fr>]

After a new install, things went like this:
Gnome started and everything was OK.
I rebooted and then Xserver would not start due to :
dev/psau not existing.
I reconfigured xserver, changed psau to ttyS1, which is what it should 
be. Then Xserver started OK, but without mouse.
I re-installed the complete system, and while everything was working, as 
for the first install, I looked at Xserver log:
dev/psau and mouse imps2
After rebooting same problem, no dev/psau
I then tried another mouse on a USB port, changed to dev/input/mice and 
it was OK.
Any idea how to solve this problem?

Anyway, congratulation for the new bootstrap with a testing debian, 
great job.