Many corporate laptops come with a Microsoft Windows license. Often the serial / key is embedded in the BIOS so if/when you format/re-install it will be automatically licensed/activated.

I had a few dead HP Probooks I needed to retrieve the license key from; I was able to dump the BIOS (see notes on an earlier blog entry then it was a case of scanning through lots and lots of garbage to find what looked like a valid serial. I eventually found it around address 00B14AE0;