I think what you need to do is send the byte value for STX which I think is 02 hex. There are a few ways to do this. The easiest way to do so is to right click on a text control and select hex display. Now type 02. Change it back to normal display if you want to type in the rest of your message. Connect this control to serial/VISA write. This should be the same as type "ctrl+b" in HyperTerminal.
Let me know if this doesn't help you.
Brian