If you are using the Gnome live cd, go to Preferences>Mouse and tick the enable Tap to Click box. If you are using the KDE live CD, open and terminal and type:
In KDE this is good for the session you are in, but must do it each time unless you change the hal policy (I believe), which of course you would not do with a live session.
Fedora disables tap-to-click by default for some reason.
Bob