If the 2008 server is running the WSUS server software, then WSUS handles the download of updates to its repository internally. You can check the status of this from the WSUS server console under Administrative Tools.
For the underlying server itself, it behaves just like any other client server and will talk to the WSUS installation to obtain its updates. It should show up just like any other client on the WSUS console.
If the problem is with WSUS itself not being able to obtain updates from the internet, run through the WSUS server configuration wizard (via the WSUS console) and there's a step that should test the connection out to the Internet. Problems here are usually due to firewall restrictions between the server and the Internet.
If the problem is with the server OS getting updates from the WSUS install, check the WSUS event log in c:\Windows\SoftwareDistribution\ and see if there's any more info about the error there.
If you want to reconfigure the server to go directly to Microsofts update service, and ignore the local WSUS service, edit the update settings in the registry under:
To reset this you can delete the AU key, and it will be re-initialised on a reboot.
If none of this solves the issue, next questions would be:
- How is the server 'tied' to the WSUS server? Via a group policy, or manually via a registry entry or the command line?
- What's the last 10 lines of reportingevents.log in c:\windows\softwaredistribution