When I bought the PC, it came with the Windows 2000 OS CD. Unfortunately the CD was damaged by mistake. But I still have the licence CD key. Is it possible to get another copy of Win2000 from MS with the same licence CD key?

I seriously doubt it, I think if you caused the damage they won't do anything. If you still have the original packaging and the original damaged disc maybe, call or email them and see if they will replace it if you send them the damaged disk and the packaging.

FYI, MS support for Windows 2000 has expired. So you may not be able to get a replacement cd, but of course try. :)

Here is an excerpt from the Wikipedia entry (http://en.wikipedia.org/wiki/Windows_2000):

The Windows 2000 family of operating systems moved from mainstream support to the extended support phase on June 30, 2005... Microsoft continues to provide critical security updates on a monthly basis and pay per incident telephone support. However, free technical support and design changes are no longer provided... All Windows 2000 support including security updates will be cut off on July 13, 2010