A successful registration is one where the record is created... process of registration is completed. Payment method does not matter.
MyScript is currently pretty simple and does not have any preset parameters. You create your own code and insert it into the plugin... then it is run after the registration is completed.
I'm testing the plugin MyScript but my code does not seem to run. I tried displays ("echo 'Hello World !', redirects (" header (' Location: [url=http://www.google.fr']http://www.google.fr'[/url]);"), assigning session variables (" $ _SESSION = 'Hello World !';") or even bad code ("test ("). But when I register, I never have any sign of the script. I receive the registration confirmation by e-mail.
My test is a registration for a test event with a later payment (payment by phone for example).
I use Joomla! 1.5.15 with DT Register 2.6.3a and MyScript 1.0.