I had the need to load a MSSQL 2000 instance on a Windows 2003 box when I encountered the following error “Unable to validate product key”. This was the MSDN SQL 2000 CD that I had used on numerous W2K and WXP boxes so I had no idea what was going on. After some researching I found the fix.
A simple registry change. The hack can be found here.
I hope this helps someone else out.