If you get the InnerXml of the Rich Text node, it will be parsable XHTML content. You can load this into a seperate DOM object and browse through it just like any other XML. Once you have this setup, you can query with XPath to find all of the <b> elements, and then copy their contents to the other field.
Hope this helps! Please copy the code here when you get done, I'd be interested to see it.
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge