Vista - Virtual PC and ExpressCard EVDO network access

I am trying to get my Virtual PC (running XP as gust on a Vista host) to
access the net over my Verizon EVDO broadband aircard, an ExpressCard device.

The guest OS doesn't see the ExpressCard at all, so I can't install the
drivers for the card. And the device does not show up as an available adapter
in the VirtualPC network menu.

In theory, however, I should be able to use shared networking (NAT) to get
to the network on the host machine and from there out to the rest of the
world. I can do that when I am connected by Wi-Fi, which happens to have an
integrated controller on the motherboard and which is available as a
networking adapter in the Virtual PC networking setup.

In fact, when I have shared networking and my aircard in, the guest OS
believes it gets a valid IP from DHCP, but it is impossible to manually ping
the gateway which is also the IP of the DHCP server as seen from the ipconfig
/all.

I have turned off all firewalls and still get the same behavior.

Any suggestions?