Instead of having registries, OS X has libraries. There are two libraries, the system library and your user library. A library is basically just a folder with some text files in it, which are used to hold your settings.
The filenames in the library follow a pattern - com.company.product.plist. If you install two copies of Office, you'll still only have one com.microsoft.office.plist, so you'll be fine 🙂
NB: This is vastly oversimplified.