You're talking split tunneling.
If you're familiar enough with the command-line ROUTE.EXE tool, you may be able to examine the routes placed by the VPN client, and remove them. You'd then re-add one to allow just the traffic to your corporate LAN to flow through the VPN gateway.
Specifically, you'd use
...to get a list of the routing entries. Without seeing the output, it sounds like your VPN client would have placed a default (0.0.0.0) entry with the gateway being the VPN peer gateway.
You can use
route delete 10.*
...for example, to delete all entries pointing to a 10.x.x.x network.
You can then use
route add 10.0.0.0 mask 255.0.0.0 10.0.99.99
...where the first address (10.0.0.0 255.0.0.0) is your corporate network and mask, and the second address is the remote gateway.
You would need to run this each time you connect, so you may want to script it.
Side note: an alternative would be to convince your company to set up their VPN to use split tunneling; an argument for this is reduced bandwidth, and (IANAL) reduced liability for non-corporate web traffic flowing through their network.