[Brian]

You'll only be able to have the app running on one machine at a time, but our license agreement actually allows you to install it on multiple machines. Just choose the "Personal" license type when you enter the registration code on the second machine.

If you still want to remove the license from the first machine, just select OmniPlan -> Licenses... from the menu bar. Select your license in the window that appears, press the "Delete License" button, and you're all set.