I've been getting irritated with the touchpad on this new Dell Vostro 1400. I type for a while, and then my palm touches the touchpad, sending the pointer skimming into the line above, or clicking on buttons I don't want to click on. So, I looked around and figured out a solution. Over the past two years, I've had to update this post for every single new version of Ubuntu, which has been a pain, so look for the heading below which corresponds to your version of Ubuntu.
Ubuntu Hardy 8.04
First of all, you need to edit your /etc/xorg.conf file, for which you'll need root privileges – use sudo.You just need to add one line in the input device section, which is the one in bold below. (Intrepid 8.10, see below)
Identifier "Synaptics Touchpad"
Option "SendCoreEvents" "true"
Option "Device" "/dev/psaux"
Option "Protocol" "auto-dev"
Option "HorizEdgeScroll" "0"