A friend of mine bought a laptop from ebay the other week. Arrived with no problems. Very friendly seller. The laptop had the hologram Windows XP CD Key sticker on the bottom of the laptop too
He came across a problem and had to patch windows XP to SP1. After applying the patch and rebooting XP then asked to activate windows again. So it generated a product ID code. He phoned Microsoft, and got some chap from Liverpool. He gave him the product ID code and the microsoft chap then reeled back the activation code which my friend entered into the laptop, hit enter and the screen went blank. He told the Microsoft bloke what had happened, and he hung up on him. So my friend phoned back since it had appeared Microsoft had broke his computer ??? He spoke to another bloke at Microsoft and got told that it was an illegal copy he was using and was given the nuke code which is given out to people that attempt to activate an illegal copy of windows xp. The nuke code appears to fdisk your hard disk basically deleting your primary hard drive partition.
So the laptop had a genuine CD key on the bottom of the laptop but it had a dodgy copy installed.