Helping people with computers... one answer at a time.
Microsoft is configured to run only one version on a computer at a time. It would likely become confused if you tried to configure two versions.
Can I get email attachments to open in Word 2007, which I have installed on my computer, instead of going to Word 2010 which is also installed on my computer when I purchased it, without taking Word 2010 off of my computer?
In this excerpt from Answercast #14, I look at the possibility of running two Microsoft Office versions on one machine at the same time.
Very short answer, no.
Microsoft Office is not very good about keeping multiple versions of Microsoft Office on a single computer at the same time. Specifically, you need to choose which one you want: 2007 or 2010, and uninstall the other... if it's there. If you were able to install both, my guess is there's more to this that's not working than you realize.
Microsoft Office in general (and that's specifically for Microsoft Word, as well) does not really play well with previous versions of itself. It really does expect that one, and only one, version will be installed on your machine at a time.