I finally found a solution to the infamous problem of not being able to disable the Inspiron's touch pad after I upgraded from Vista to Win7 32bit.
I had to install an older touchpad driver to make this work. The driver is Dell R165804, this driver is labeled "Dell Touchpad Driver for XP/2K and Vista 32" when I installed it in my Inspiron 1545 it added the Dell Touchpad tab to my mouse settings under the control panel. Then I opened the control panel, clicked "mouse", under the Touch Pad tab click on the picture of the touch pad. I was then able to click "Device Select" and check the box that says "Disable Touchpad when external USB device is present".
Now when the USB mouse is attached the touchpad is disabled and I don't have my cursor jumping around while typing due to my fat thumbs touching the mouse pad.
Hope this helps someone else out there!