VirtualBox Share Guest Internet With Host
In order to get this working, you'll need to setup "Internet Connection Sharing" in the Windows 7 guest. You do it like this:


Open Control Panel => Network and Internet => Network and Sharing Center
Click Manage Wireless Networks in the left sidebar
Click on your USB WiFi connection, and then Adapter properties at the top
Select the Sharing tab and check "Allow other network users to connect through this computer's Internet connection"


Now your Mac host should be able to use your virtual connection to the guest to access the internet. If you want, you can set the host to use DHCP on that connection to get IP address, gateway and DNS information automatically.