I know how to do it using LabVIEW. I suspect it will be very similar in VB.
You need to provide a 5 V TTL pulse from your handswitch, and wire it into the trigger input on the card.
When you set up your acquisition, configure the trigger to start the acquisition. It is fairly straight forward.
Another possibility is to monitor the trigger input, and acquire the image when the trigger is registered. There would be a small delay due to software, but it would be minimal (a fraction of a second). This way, you could display a live image, then store the current image when the trigger is detected.
Bruce
Bruce Ammons
Ammons Engineering