Hm, If its already a home server. you could just activate openvpn.

and use n900 to connect to it.

The most simple one:
1. use remote desktop or vpn from XP
and open the port in your router
and you should be able to use remote desktop or vnc from n900 to your home machine.

Once thats succesful, you could always change it to use openvpn.