You can either use the Shared Networking (NAT) option or you can select your Airport card in the network settings panel.
VPC will use it as a standard NIC, not a wireless NIC, so it should grab an IP from your router/dhcp server just as usual.
EDIT: I should add that OS X will control connecting to a wireless network, so as long as it is connected, your VPC guest OS should get an IP. If OS X has issues connecting to an AP, then your guest OS will consider it to be a disconnected link.