To be more exact, you should run RegTool program from SYS:Tools directory. Computer has to be connected to internet to get it completed, but you can run it from live CD or HD installed system.

RegTool asks couple of questions and finally sends you PayPal link for payment with email. When it is paid, you get your keyfile in email. It doesn't matter who pays the bill, until it gets paid... so if you don't own PayPal account, you can ask anyone to pay it.