cant use office 2000

You might as weel do a reinstall and select "Run All From My Computer" for each and every product you want to use. Then leave the CD in the drive and open Outlook because it will still want the CD. How M$ can get away with selling this buggy installations anymore is beyond me.
Then as soon as you reboot get ready to uncheck the box on the "Optimizer" as it will lock you up tight.

Microsoft has all these ridiculous rules for installing and running Office with multiple users. It can get very confusing. In your particular situation, usually installing Office 2000 a second time will kill that error message. Check out this link to the MS knowledge base that deals with your error message.

http://support.microsoft.com/default.aspx?scid=kb;en-us;233529