Help with restricting access to VPN WRT54G

It's not the router that will be doing it. What VPN client will you be using on the laptop? Any modern day VPN client (Nortel, Cisco, etc) enforce policy. So, when the laptop connects to the corporate network using the VPN client the laptop is now restricted to only accessing things on the VPN.

When you make a VPN you are creating a tunnel - a private network (if you will.)

It sounds as if you need to get a fundamental understanding of how VPNs work.

Once your laptop is tunneled into your corporate network the VPN termination point inside the corporate network can enforce policy on the clients that connect to it. I.e., do not allow split-tunneling, etc.

When the laptop starts the client and connects it is no longer (logically) on the local network. You can test this yourself when you start the client and connect to your company. Ping your local PC's, etc that are on your Linksys router - you will not be able to and neither will those clients.