Well, you obviously created a mess for yourself. Whatever you downloaded was not an official edition of MS Office 2003; MS Office 2003 simply is not distributed that way. You have to buy it on CD.
I'll suggest an initial procedure to try to resolve this; it may not work, but I suggest trying it and then, if it does not work, other measures will have to be taken. Uninstall MS Office 2000 Prof again, download, install, and run
CCleaner. Use all the scans in CCleaner, the Windows scan, the Applications scan, and the Issues scan. When CCleaner asks whether you want to back up your Registry before removing items found in the Issues scan, reply with Yes and do the backup. Then, reinstall MS Office 2000 Prof and see whether it works.