Your question is not very clear... Neither Office 2003 nor Office 2007 will
run on the Macintosh OS X operating system. Those versions are Windows OS
only, so I don't understand where Mac comes into the equation. The documents
created by the various versions of Office can be transported from one OS to
the other, although there are some considerations in order to do so with a
minimum amount of disturbance to the documents. Those considerations,
however, aren't really anything new or extraordinary with few - primarily
graphics related - exceptions.
That being said, you can use Mac OS X Boot Camp to create a Windows
partition & boot the Mac (Intel Only) as a Windows PC, in which case you can
run Windows software.
Alternatively you can install one of various Windows emulator applications
(Parallels, VMWare Fusion, CrossOver) to install Window & Windows software
as a virtual machine. This allows running Window & Mac OS X "side-by-side" &
switching back & forth between Mac OS & the VM, which Boot Camp doesn't do -
you boot into one OS & need to reboot in order to use the other.
Either way, however, you're bound by the EULA for any installation of
Windows as well as the PC software you use. IOW, you legally can't install
the same copy of Windows on a PC & a Mac any more than you can install the
same copy on 2 separate PCs unless you purchase a multi-license package.
Out of curiosity, what "functions" do you need from Office 2003 that aren't
provided in 2007?
HTH |:>)
Bob Jones
[MVP] Office:Mac