Jamie,
First, you're a programmer for ann HSP that does installation fulfillment for [satellite television company]. So am I.
Second, I've jumped through the hoops you're jumping through right now including capturing work orders, inventory management, route sheets, etc. I also use ASP for development.
That said, let me address this specific problem.
Yes, you can be logged in to the VPN and connect to your local network simultaneously. The two-network-card trick will not work. What happens is that both network cards will be assigned IPs by the VPN. However, you can bypass this by installing another network protocol such as IPX/SPX. You can still use mapped drives and whatnot, but you will not be able to print to network printers over TCP/IP, etc.
Put IPX/SPX on a test box, then a target box. Log into the VPN on the test box, then try to connect to a share on the target box: e.g. in the Windows Explorer address window put \\TARGET_BOX_NAME\SHARE_NAME then press enter. Viola!
Now your folks can use your internal database to decrement receivers from inventory. However, there are easier ways of doing that, some 48 hours delayed (CFH_DAILY reports) and others near-real-time (which I won't go into on this forum) that won't require data entry by your call center folks.
Good luck,
Sean Clifford