I'd like to (easily) connect a WinXP machine to another LAN that has a Vista
Home Premium box and two XP boxen.

I run an ordinary ADSL modem that connects to a Linux box for routing the
LAN here (the other machines here dont need remote access), and at the other
end they have an all in one modem/router. So, we're both doing NAT; I really
dont want to start messing with port forwarding.

Is there anything that will do this? The goal is to share desktops and do
remote maintenance.