You need to reinstall the driver for your touchpad. Log onto Dell Support and search for drivers, and get the touchpad driver, install it, and in that control panel you'll find the way to disable tapping.
I have a dell inspiration 1100...and when I first got it I did not like the Idea that you can left click just using the touch pad and somewhere I found how to disable that feature.
But it seems that something maybe SP2 enabled that feature again and I can not remember how to disable it again.
I did get the latest driver but that did not help.
Can anyone help me disable that part?