How do I turn touchpad off when I plug in my mouse?

I had a setting on my old laptop that automatically turned off my touchpad when I plugged in my usb mouse. Unfortunately dell came to fix my audio and broke the entire thing... So i made them send me a brand new computer Dell Latitude D830 with Windows XP Professional. Now I can't find that function in the control panel. The mousepad is a Dell Touchpad Alps version 7.1.101.6 and is plugged into the PS/2 mouse port. That is all the info i can give... please help!!! i keep touching my touchpad and clicking random **** while typing and its driving me nuts!!!!