When you install Windows Server (Longhorn) 2008, if you wish to connect to the internet through a wireless card you need to perform a few steps first.
The server is completely locked down when installed, which is good for servers, but bad for ease of use.
Open up Windows Firewall -> Select Exceptions Tab -> Select Network Discovery. Click OK.
This will allow Windows to discover networks that you are connected to. This is important for connecting to the internet.
Open up Control Panel -> Go to Network and Sharing Center -> Under Sharing and Discovery click Network Discovery -> Click Turn on network discovery -> Click Apply.
Now you should be able to connect to a workgroup / wireless router.