I haven't used this program myself but you might try installing a program called "tpconfig" and playing with it. It is supposed to let you configure touchpads.

I can't do anything useful with tpconfig. But gsynaptics works, after you do this: http://linux.dell.com/wiki/index.php/Ubuntu_7.04/Issues/Changing_mousepad_settings Except that it does not work for sensitivity on my D620.