I've never used visual basic, so you may not want to use this. But an easy way of communicating between languages in through the use of files.
Check out processing @ http://processing.org/
It can read serial data, just like the serial monitor, and it can output via files.
So you could do this:
Arduino prog---Serial out-----processing------file------visual basic
I'm pretty sure vb can read files, though... most can.
And then you could have a tx and rx file: tx.txt and rx.txt
Processing (or sh) could read the tx file from vb and send it to arduino, processing could output arduino serial data to tx file, which vb could read.
I'm sure there is an easier way, so as I said, only use this as a test. DON'T put it in your final design.... it is probably quite slow.
Sorry if its confusing.