my cousing just gave me his laptop for free, and it was running a windows 7 license. I would like to know if I can keep that license and use ot on another machine that I'm going to build cause I want to try a few linux distro on that laptop
Assuming that it is an OEM license that came with the machine, then it's not allowed because such a license is tied to the machine.
Now, one /could/ "theoretically" try to use that license to activate Windows 7 on another machine, have the activation complain and show you an activation service phone number, punch a lot of numbers for a robot operator to (usually) accept that the reason for the major change in hardware to be because of a "repair" of the system. But you would have to have used an OEM installation disc of the correct edition of Windows 7, as a standard full license or upgrade installation would not likely accept the key under any circumstance.