Hi and welcome to the InfoPath Dev forums.
You should be able to do this, I just created a little sample in InfoPath 2007 and attached it so you can see how it works.
Perahps you have a setting on the richt text field (in the properites dialog box) which is causing this to not work as expected?
After you look at my sample you could post pack your template so I can take a look if you still can't get it working.
Ted