Not unless you want to.
If you've got an Upgrade version of Office 2003, you shouldn't, as the
upgrade installation will doubtlessly check to ensure that you've got a
qualifying product installed.
If you've got a full version of Office 2003, you can (should you want to)
install both on your machine. If you choose the normal install (or whatever
it's called...), Office 2003 will probably try to uninstall Office 2000 for
you, but you can override this behaviour by doing a custom install.
