That would depend on the version of RoboHelp that you are using, which is why we ask people to state that in all new threads. See Before You Post.
If you are talking about RoboHelp 8, then it is easily done. See the RoboHelp Tour on my site and look for the bit on iFrames.
I think it can be done in earlier versions but may be more tricky. I know someone who will advise on that if you do post back saying you are using an earlier version.
See www.grainge.org for RoboHelp and Authoring tips
Yes, I'm using RoboHelp 8 and the explanation on your site did what I needed. Can the frame size (in red below) be dynamic to fit the content?
style="width: 80%; height: 100px;"