Graeme,
You should be able to use the standard PPTP VPN connections from WIn XP. I have a XP user with a laptop who VPNs into a 5.6 server easily. There are various things around here about using IPSEC instead, along with comments as to the security of each - I think that IPSEC is meant to be better. Personally, they don't have that any state secrets hidden on their server so they operate an 'acceptable risk' policy.
The only fly in the ointment MIGHT be the Netgear router. They originally had a Netgear DM602 single port router which steadfastly refused to accept incoming VPN connections. You could easily VPN out through it to A.N. Other server, but there is something in the firmware that blocks incoming on GRE port 47. This wasn't mentioned on the documentation.
I spoke to Netgear and they acknowledged that this was a problem with the router and offered a very 'beta' firmwar hack - something to do with the way it does NAT I believe. I decided against it and bought a Vigor 2600 instead. A doddle to setup and use and so far very reliable.
HTH
B. Rgds
John