Word 2007 is installed, can Word 2003 also be installed on same PC

Hi there,
I'm hoping I might be able to get a definitive answer in relation to having both Word 2007 (currently on the computer) and Word 2003 (yet to be installed) on the same computer.

Owing to some MT work that uses complex macros Word 2003 must be installed. The user already has Word 2007 installed on her computer. Unfortunately, Word 2007 came installed on her system and she does not have backup discs. She is therefore reluctant to install Word 2003 in case it interferes with Word 2007 which she uses for most of her work.

I was wondering if she could perhaps install Word 2003 on a portable external hard drive? She could then keep it separate to her PC's installation of Word 2007.

I'm not sure if this is possible and would really appreciate advice regarding this.

Many thanks,

ozgal