Hi, I'mCustomer Welcome to JustAnswer. I'm reviewing your question now, and will post back with your reply ASAP.
What is the model and brand of your old computer, also can you connect your old computer to the Internet ?
Unfortunately you need to connect your XP computer to the Internet, once done, Open CS3 and choose Help > Deactivate or Help > Transfer Activation. select Erase My Serial Number From This Computer. When you see the Deactivation Successful message, click Exit.
If you can't connect the XP computer to the Internet then you need to contact Adobe cutomer support.
Let me know if you need further assistance
Do you still need help please?
If you have further assistance please reply back to me and i will gladly continue to help