I have bought used computer with license sticker for win xp sp3 media center. System needs to be reinstalled. I do not have win xp sp3 media center CD. Can I install win xp sp3 and use key from the sticker?
Thanks in advance for help....

I could be mistaken, but I do not think you'll be able to use the same product keys, especially if the media you have is OEM.

So that key can not be used? I have heard that win xp sp3 media center CD has never been sold in a free market, only with systems in wich it has been installed. How could I get win xp sp3 media center installation CD?

I did a quick search on nextag and found a few selling for about $80. Back to whether the you can use the key you have on XP Pro... I am about 99% sure you cannot, but why dont you just try. Rather than trying on your system by re-installing, install virtual PC or similar virtual application on your current system, and install XP Pro as a VM, then try to apply the key you have. If it works...great, if not, just delete the VM and go to plan B which is buying another copy.