See merged projects in the help and on Peter Grainge's website (grainge.org)
Jeff seems to be confused. Merging and combining are two entirely separate things.
To combine two help files, you take different actions depending on the source and what is being used. (RoboHelp for Word or RoboHelp HTML)
If you are using RoboHelp HTML, you just right-click your HTML files area in the Project Manager pod and import the topics from one project into the other. Then you amend your Table of Contents and Index to include references to the new content.
With Merging, you still have multiple help projects. As I understand the question, that's not what Michelle is wanting to do.
Helpful and Handy Links
Sorry, my mistake - I don't do either one of them ;>)
Thank you so much! I'm going to try combining today!