Mouse: Is it plugged into a serial port (little D-shaped plug)?
Is the serial port enabled in BIOS?
No, it's not little D-shaped plug...it's similar to a monitor plug.
(*) Mounting Screw
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/ |
| + + |
| + + | Nine prong female
| + + |
| + + |
\___ + |
(*)
I only had a quick look at the link and it seems to be helpful...
Thank you for your help so far, I'll keep working on it!

Cariboo
EDIT: Feb.03,08
More Help needed

I'll separate this thread in two:
1) Mouse Pointer visible but not movable
2) Install USRobotics ISA Modem
UPDATE: Feb. 24, '08
Mouse and Modem are working (I write this from that old machine)!
New problem:

3) Cannot mount CD-ROM drive! (New thread)