Upgrading WSS 3.0 to Windows Server 2008
Since this is probably the most common scenario that enterprises will face, here is a link on how to upgrade WSS/MOSS (SP1 only) on Windows Server 2003 to run on Windows Server 2008.
And here is the larger resource center on TechNet dedicated to Windows Server 2008 and WSS/MOSS
https://technet.microsoft.com/en-us/windowsserver/sharepoint/bb735844.aspx
In the upgrade scenario, critical items to note include disabling and stopping osearch to avoid corrupted indexes during the Windows upgrade.