Not sure if this thread is still active.

I worked through a similar situation. As I understand it (correct me if wrong) you will have them make text bold face by either typing without bold, then clicking an icon to make it bold or typing Ctrl+B (i.e. for most text editors).

In the text entry field, you change the attributes by changing the shortcut key to allow mouse clicks, and attach a keyboard shortcut that is Ctrl+B. Then in the options tab for that click box, checkbox the Show Button option (then you will make this button transparent and put it over the software button that bolds text). Finally, tell the on success to Continue.

You could have on-screen instructions telling them to type a certain word, say "pancake." Then, after they type it and either press Ctrl+B or press the bold button, you would make the demo continue and have an image/slide that replace the text field with the bold text. This creates the illusion that what they just typed in fact became bold.

Its a little mickey-mouse, so I hope that's clear.

It sounds to me like your looking for text editing functionality (bold, italics, etc) to be included based on a users input.

I don't think in Captivate this is possible, but you could pretty easily export to Flash and create that bold functionality pretty easily using a textbox and htmlText formatting. You would just take the text entered into the text box and wrap it in bold tags and enter it back into the textbox which accepts html formatting.