Windows 2000 won't open

My second time around trying to get an answer to my Windows 2000 trouble. To make a long story short: Dell 4300 Dimension, Windows XP. When I try to open Word it tells me "This application must be installed to run." I have tried reinstalling Word from the original CD and reinstalling all of Microsoft Works from the same CD. No luck there. I tried the normal.dot thing where you go in and rename it. I tried downloading a new Windows Installer. Neither of those things worked either. I'm wondering: Would it work to go into the registry and delete all the Word 2000 files and THEN try reinstalling? Or would that do some irrevocable damage? One more thing: When I reply to an Outlook e-mail, the computer tries to install Word 2000. (It doesn't get very far, but it tries.) Could the e-mail program be the problem?