First, PGD9 is now quite an old version. However, I assume from your thread title you are wanting to run it under Windows XP, is that correct? Given that XP is no longer supported in any way by Microsoft, are you aware of the potential dangers of continuing to use it, especially if it is ever connected to the Internet?
Assuming you already have a Magix account, go to this page, log in and go to My Products. You should find the installer and the serial key listed there. If it is not, you will need to email infoservice@magix.net and ask whether they are able to give you this information.