Did you try the Number property for the Text Box? Right click in text box and select Text Box Properties. On the Number pane, select Number or Currency in the Category field. (Currency if you want the money symbol). Set the decimal places and the 1000 separator value.
I'm pretty sure this won't work if the value is not a numeric, at least I haven't had any luck formatting strings even with the conversion functions.
[font="Courier New"]Looking for a Deadlock Victim Support Group..[/font]