You are creating a LV driver when you use the VISA functions. Joe's
suggestion to try it in Hyperterminal is a good one. I noticed that
you do not mention either VISA Configure Serial Port or a VISA Write.
Once you verify baud rate, stop bits, etc. and the cable with
Hyperterminal, you should put in a VISA Configure Serial Port with the
same settings as Hyperterminal. If the instrument sends out a constant
stream of data (which you can confirm in Hyperterminal), then you
don't need a VISA Write to tell the instrument to send something. If
it doesn't, you'll have to first write that command and then do a
read.
