I've read that you can install Office 03 & 07 on the same computer if on installation you choose a location other than the default. The registry entries for Word I've had to track down have been in "folders" labeled w/ a version number, so maybe simply setting up a different folder under Program Files than the default on installation would work. There might be some problems in the docs & settings > user > application data > Microsoft > Office, Word & Templates folders, tho.
I run Word 2003 in a winxp virtual machine [VirtualBox] on a mac w/ Office 2011 installed. I prefer Word 2003 to Word 2011 [it's much more customizable] but there's no Office 2003 for mac. I don't know if you'd have to have two winxp licenses to run a virtual winxp on a winxp machine - I'd think not. Keeping two winxp's security updated would be a pain, tho. You'd really have to want/need both versions available to make it worth the effort.
Edited by MaryBet82, 26 February 2011 - 01:33 PM.