Here is a link to a thread on a recent post showing how to communicate serially to an Omron PLC using VB.Net. This uses the Omron Host Link serial protocols. (C-Mode Commands) It will read 10 DM registers and display them on the form.
Here is the source program that can be downloaded.
VB6 Program: http://accautomation.ca/how-to-implement-the-omron-plc-host-link-protocol/
VBA Program: http://accautomation.ca/how-to-implement-the-omron-host-link-protocol-part-2-vba/