Router – attach a VPN firewall to an existing network and have it manage VPN connections

I'm quite new to networking and am trying to set up my first VPN connection.

The Situation:

I have been contracted for some programming at a facility some distance from my location. I would like to be able to set up a simple VPN connection to their network so that I may make adjustments without significant travel.

Their Current Network:

Six devices (one I need to connect to) plugged into a basic router (Dlink). This router has an internet connection and a static ip address.

My Hopeful (questionable) Proposal:

I attach a VPN Firewall I happen to own (Netgear FVS318) as device number seven on the client network. I disable routing / DHCP in the Netgear. I forward the appropriate IPSec ports from the Dlink to the Netgear. I then create a VPN connection on my office Windows 7 machine to the remote network. The request is forwarded from the Dlink to the Netgear where the VPN connection is authenticated. I now have a remote-access connection from my office PC to the client's local network.

The Question:

Will this proposal work? If not, would another possibility be to attach a computer with a VPN server to the client network?

Also, as a note: the client has requested I not replace their router or place mine in-between theirs and the internet 🙁

Thanks very much!

Updates:

2012-06-04-0844:

Been trying to test proposed setup with no success. Not yet sure if problem is with network organization or connection configuration.

2012-06-04-1240:

I can access the Dlink network when I do one of the following:

• Place the Netgear VPN between the internet and Dlink (although this is NOT allowed by client)
• Attach a computer running a VPN server to the Dlink network

I cannot, however, create a VPN tunnel when just using the Netgear VPN firewall as another device on the Dlink network.

This leads me to a tentative answer of "No, attaching a VPN firewall to an existing network does not seem to be enough to create a remote-access VPN."

2012-06-04-1617 (final update):

Thanks @MikeAWood ! My proposed setup will not work as desired because the Netgear is designed to tunnel from the WAN to LAN. I instead implemented a solution by connecting an additional PC (with a VPN server) to the Dlink network.