- Open /usr/share/X11/xorg.conf.d/50-synaptics.conf (as root) in an editor.
- Add the text
Option "TapButton1" "1"
Option "VertEdgeScroll" "1"
- Save, reboot and enjoy.
If you don't like the idea of changing system config files, you can use synclient in a startup script to enable things as well.
 At least at the time of this writing. When Squeeze is eventually released, this may change.