VPN between 2 networks with same subnets

I have a VPN set up at home which is sat behind a Vigor 2820 router.  The local network there is 192.168.0.xx subnet 255.255.255.0.  This works fine usually but I now have a problem that I am using a network in a building which uses the same values.  I guessing this is why I cant see anything because the routers dont know how to route!  I would prefer not to change the ip addresses at home as it would mean readdressing everything and im only here for a few hours.  I obviously cant change anything here as although they are happy for me to use their internet I think changing their addressing would be a little rude!  Is there any way of getting around this problems as I guess it will crop up in the future (192.168.0.xxx being such a popular range)