Remote Access routing advice please

[chillari]

I have a client I need to support remotely whoes security nazis wont allow me to VPN into, & standard dialup isnt an option for what I need. There RAS system uses a Lucent ISDN based dohicky, so I can connect at 128k which will do the job for me. Now the nazis on my network, wont allow me to put a machine on out network that could be a potential back door (fair 'nuff).
I need the internet based access so that I can connect from home via cable or PPC via GPRS (glad i'm not paying the phone bill).
The best solution we came up with is a standalone PC in the office with an ADSL link & an ISDN (demand dial) link to the client.
Now here's where my problems start, what I do after connecting to the standalone gateway box from the net. I see 2 alternatives.
1. Running VNC server & taking control of the machine, making the ISDN connection & proceeding as If I was working locally. This will be easier to configure but will only allow 1 person to connect which will be ok for 95% of the time. Also having VNCs within VNCs will get messy
or
2. Making a VPN connection to the gateway maching (Linux) & using routing to connect to the client. Configuring this option is where I may need a little help with the routing.

TIA
Joseph