My Dell Latitude E6520 (Windows7) did not have an option for me to disable 'Tap-to-click' on the Touchpad. The available options under the general mouse keypad had no such option included. I had seen similar issues, with other Dell laptop models, and in those cases a BIOS update had sometimes been called for, but in most cases that was like hitting a nail with a sledgehammer, so I figured there was probably an easier way to proceed, and there was.
1) I went to http://support.dell.com/support/downloads/driverslist.aspx?c=us&cs=28&l=en&s=dfb&ServiceTag=&SystemID=LAT_E6520&os=W764&osl=en&catid=&impid= and downloaded and installed the DELL_MULTI-TOUCH-TOUCHPAD driver for Windows7 64-bit.
2) After restarting, the Dell Touchpad icon showed up, in my system tray, but it would not work without the .NET framework installed.
3) I went to Microsoft, got the latest v4 of .NET (client side), and installed it.
3) The Dell Touchpad control now functions and I was able to disable tap-to-click easily.
The addition of the 'Dell Touchpad' tab after installing the Dell update and .NET: