Which version of CM7 are you running now? The youtube video points to CM7.0.3. There is a newer, *MUCH* better stable version, CM7.1.0. You can get it here:
CyanogenMod Mirror Network - Powered by TDRevolution
Also, do you now have a back button? If it's still AWOL, go to Settings, CyanogenMod settings, Tablet tweaks, Choose soft-buttons.