Office 2000 Small Business Editon is supported by Vista 32 and 64 bit versions. I use it fully updated every day with numerous Vista systems. Will Vista support two versions of office on the same computer? As long as the two versions are Office 2000 or later, Vista will support everything XP does.
Install 2007 first so that it will not 'upgrade' the 2003 install. I have 2007 Home and Student edition with 2003 Frontpage
Installing 2007 second is the way to go, it will actually come up with the option to upgrade or new install in the setup, same as what 2003 did with older versions. Sometimes installing the older version second will stuff up the newer versions install and youll only have to install it again anyways.