Ben Armstrong writes on his Blog site that the Virtual PC team decided to NOT enable networking on wireless network adapters in Virtual PC 2007, by default.  Reason being, Virtual PC's hit or miss support for wireless networking in the past.  Ben writes:

To enable this on a Windows XP system you’ll need to:

1. Open the Start menu and click on Control Panel.
2. Click on Network and Internet Connections and then Network Connections.
   
   If you are using classic mode you just need to double click on Network Connections.
   
   
3. Locate your wireless network adapter, right click on it and select Properties.
4. Check the Virtual Machine Network Services entry and click OK.

On a Windows Vista system you’ll need to:

1. Open the Start menu and click on Control Panel.
2. Click on the Network and Internet and then Network and Sharing Center.
   
   If you are using classic mode you just need to double click on Network and Sharing Center.
   
   
3. Click on Manage network connections, in the task list on the left side of the window.
4. Locate your wireless network adapter, right click on it and select Properties.
   
   You’ll need to approve this action.
   
   
5. Check the Virtual Machine Network Services entry and click OK.

Check out Ben's original posting on his site, and leave any comments for him there as well.