It will install on any hardware (Windows 2000 specifications) but Gateway own that key through MS, and have re-distributed it on. Therefore MS support will expect (demand) that your computer is a Gateway computer, if you call for support.
Theoretically it'll work on any
Practically it is only licenced for Gateway computers.
Dell/ HP Acer and others (no doubt) all have their own keys too.
Usually the COA sticker says their name as well.
So if you attach the COA sticker to a non Gateway, and sell the system, someone may notice Gateway written on it, and complain. (for some reason)