add field to register.aspx page

Hi,

I need to make changes to how the standard register.aspx page works and in particular, I dont want to make any security foopars.

The site is one that manages suppliers and I use the standard membership asp.net provider. So far I have written an invitation page so the customer can send an invitation to the supplier to join.  This invitation creates a record in a table with a GUID and this GUID is sent the the supplier added to the link to the register page.

When the supplier clicks on the link I have sent (the guid is in the quesystring), goes to the register.aspx page and registers, I want to add them to a supplier role and link their username to a supplier database record (recorded in the invitation table).  How do I modify the page to do this?

Examples in vb please

Thanks, David