Windows 2000 Server CD – no CD key

My company was offloading some old PCs and servers to the dump. I grabbed a Windows 2000 Server OEM CD, but it doesn’t have the cd key with it. It wants the 25-digit cd key, 5 blocks of 5 characters. I’m trying to install it on my “old” computer at home for education and hands-on experience since I’m studying for the Windows 2000 server exam (70-215). Is there a way to legally get a cd key for this cd so I can install Windows 2000 server on that computer? If not, any alternative and cheap (if not free) ideas to get this installed?