Vista - route add vista

I'm admin of two networks. One Network 192.168.xxx.xxx where my computer is
located and a network 192.168.100.xxx. Between the two networks works a VPN
from ISA Server to ISA Server.

With XP I could make a connection with "route add". But now I installed
Vista. When I start cmd with administrative rights and make a "route add"
the route is visible with "route print". But all pings from that network
won't answer. I have a virtual machine in virtualpc2007 with xp and one with
vista. From xp no problem, but in vista it doesn't work.

Thanks for every answer and sorry for my english...