You can install them on the same computer, in the same partition. It's best
to install 2003 first and then, when installing 2007, to do it in a
different folder from 2003, ("Microsoft Office 2007" as opposed to
"Microsoft Office", say) and and to not accept MSP's offer to upgrade or
uninstall the previous version. The global.mpt files are stored separately
in the 1033 folders for each version under each user's folder.
Bill B