It depends on how you have networking setup. I you have it setup with NAT, then Virtual PC is assigning a private IP to the VPC (likely on a different subnet than your host PC). If you have it setup to use the same network adapter as your host OS is using, then (if I recall correctly) it should get another IP from your router, and you can try pinging it via that IP, although (if I recall) that is tricky in that it has two IP addresses using the same MAC address, and your NIC would not know where to route packets. If you have a second network card in the host, you could assign it to the Virtual machine and try connecting to it that way.
Could you perhaps post information on what the TCP/IP settings are for the host and guest, as well as information on the type of networking you have setup in Virtual PC?