One thing you can do is save your "isadora-registration.izr" file on an usb stick, you can find it under "users-->shared" and then copy it into the same folder after installing your 10.6 system.
Another thing: If you have changed your hardware to a certain amount (and depending on what you have exchanged) you have to re-register Isadora. You can do that up to three times a year. But if you have used your 3 registrations already you can ask to reset the registration count on the support page of troikatronix: http://troikatronix.com/support/isadora/
as topic choose: Registration Count Reset

Best
Michel