[MarkPW]

There is no need to modify vbulletin's files to achieve this. vB have a hook system of which allows you to execute external code at many different locations within vB's files, such as the registration or activation process.

See: What is a hook?

With regard to adding custom fields to a seperate db table upon registration - all you need to do is add a plug-in at the correct hook location (via the AdminCP), and include the code you wish to run. In this instance, you would add a hook at the following location: "register_addmember_complete" and include the database code you wish to run.

Similarly, if you only want to copy user details upon activation, you would use the hook, "register_activate_process".

Hope this helps!