It is nearly impossible to type on my Dell Latitude because the cursor jumps around anytime I get close to the touch pad. There is not a setting to inactivate it during typing. I am using Ubuntu 11.10.
This should be asked in superuser. It's typically a fn key for that in every laptop. In my case is fn f9 but yours could be other one. Just look for the key with symbol that symbolize the touchpad, maybe in blue collor or orange or any other color different that the characters colors.
I use the Touchpad-Indicator; I have it set as a startup application in Ubuntu, and it's set to turn off the touchpad.
I'm using Unity, and first had to turn on the notification area (you don't have to leave it showing there after you've set it up, but it's a convenient tool to have for turning the touchpad back on):
This allows the indicator to show in the panel.
Then install the indicator:
It works great for me with my Dell Studio.