I was leant a Dell Latitude D810 that has a Synaptics touchpad. Eventually, I had to admit that the tap-to-click setting was a little to sensitive and kind of annoying (most frequently, I accidently clicked things in my bookmarks toolbar in Firefox). I found that I could disable the tap-to-click feature by adding the line:
 Option      "MaxTapTime"      "0"
to the appropriate section of my /etc/X11/xorg.conf file so that it looks like this:
Section "InputDevice"    Identifier   "Synaptics Touchpad"    Driver      "synaptics"    Option      "SendCoreEvents"   "true"    Option      "Device"      "/dev/psaux"    Option      "Protocol"      "auto-dev"    Option      "HorizEdgeScroll"   "0"    Option      "MaxTapTime"      "0" EndSection