I'm using Debian Wheezy, XFCE4 and a Positivo MODO Black Netbook.
Method I - Init script.
Create a script with the code below and tell your XFCE to run it when it starts up.
Synclient TapButton1=1 LBCornerButton=2 RBCornerButton=3 MaxTapTime=150 SingleTapTimeout=150 MaxDoubleTapTime=150
Method II - Add your settings to X configs.
Edit the file /usr/share/X11/xorg.conf.d/50-synaptics.conf and make the Touch Pad section look like this:
Section "InputClass"
Identifier "touchpad catchall"
Driver "synaptics"
MatchIsTouchpad "on"
MatchDevicePath "/dev/input/event*"
Option "TapButton1" "1"
Option "RBCornerButton" "3"
EndSection
That's it ;-)