|OK, before you try installing 2003 make sure you have completely uninstalled 2000.|
MS has a habit of leaving Flotsam and jetsam about.
First, see here:
Second see here:
Once you get 2000 uninstalled, do a complete uninstall of the unsucessful 2003.
Once you've got everything uninstalled and cleaned out, do an new install of 2003