Tricky routing/vpn question

Kurt Granroth wrote:

> Here's a puzzle:
>
> Say you need to get an X session using XDMCP over a VPN. However, that
> VPN only has Windows client. You are using Exceed and that works but
> you would prefer to use Linux (or OS X) with a "real" X setup. But see
> above: the VPN *requires* Windows to run.
>
> So you investigate the "Internet Connection Sharing" that comes with
> Win98SE thinking that you could just do a 'route add -net' pointing to
> the Windows computer.. but it doesn't work that way since the ICS works
> using DHCP and you like your Linux box's current IP address just fine,
> thank you very much.
>
> But with that, you are somewhat stuck!
>
> Or at least, *I* am stuck. Can anybody think of a way that I can do
> some sort of redirection or port forwarding on my Windows box that would
> allow me to access the VPN from Linux?

What kind of VPN device is at the other end? I know for Cisco VPN devices you
can use IPsec on linux to create a connection with it.