Vancouv, you seem to have two issues (apart from licensing):
1) Do you qualify for an upgrade from Office 2000 Premium to Office 2007 Small Business? Yes. But you have to have an individual and unique license for each and every PC you install it on.
2) Will it be possible to perform an in-situ upgrade?
Very probably, but why not take advantage of the 60-day free trial? Do a disk image backup of your system, install the new version, check everything works and then either go back to your original image, or pay to license your installation.
SD