Windows XP SP3 Installation without Product Key
As in Windows Vista, Window XP SP3 users can complete operating system installation without providing a Windows XP product key during a full, integrated installation of Windows XP SP3.
The operating system will prompt the user for a product key later as part of Genuine Advantage.
As with previous service packs, no product key is requested or required when installing Windows XP SP3 using the update package available through Microsoft Update.

I made a bootable windows xp sp3 cd by slipstreaming service pack 3 into service pack 2 using nlite,when prompted for the product key i gave my service pack 2 product key, but it was said to be invalid,why?
U can get new SP3 product key in folder I386 that u already slipstream..
just search for file PID (setup information file)..open with
notepad and cehck for the first CD key..
FYI..this is genuine CD key..so u must activate it..or can just use for 30 days only..
Good Luck..