If you want to install and use more than one version of Office on the same computer, you must install the earliest version first.
For example, if you want to use both Office 97 and Office XP on the same computer, install Office 97 first. This step is necessary because of the way registry keys, shared programs, file extensions, and other settings are managed for each version of Office, and for the programs that are included with each version of Office.
Remember to make sure to choose Custom install for any additional versions so you don't overwrite any files from previous versions.
See the link below for Microsoft's support site on installing more than one version of Office.
Microsoft's Running Multiple Versions of Microsoft Office.
