I've just purchased a Cisco 877 to use as the router for my home DSL connection. I've set my self the task to get a VPN connection working so I can access one of my home machines when I am away ...

So I have the exact set up you're wanting and use it for essentially the same thing thing except I'm on 24x7 as the work never stops. Look for ipsec site-to-site vpn gateway/routers.

A site-to-site VPN connects entire networks together, as if they were on the same LAN. This means devices on Lab A can talk directly to devices on Lab B without jumping through port-forwarding ...