I recently updated the Ubuntu on my Dell Vostro 1510 laptop to Karmic Koala (9.10), and I had a problem: its touchpad didn’t work anymore. I found the solution on a website, and thought maybe someone else may need it.

1. Open a terminal (if you don’t have a mouse hooked up, use Alt+F2).
2.Type “su”, press Enter, and give the root password
3. At the prompt, type:

echo options psmouse proto=exps > /etc/modprobe.d/psmouse.modprobe

4. At the next prompt, type “reboot”.
Your touchpad will come back up after rebooting.

If you’ve forgotten your “su” password, type “sudo passwd”, and reset it.

Source: http://danilogurovich.wordpress.com/2009/10/17/ubuntu-karmic-koala-9-10-beta-buggy-touchpad-behavior