To determine whether you have WSS 3.0 or MOSS 2007 installed, go to Windows Start -> Control Panel -> Add/Remove Programs.
If you see 'Microsoft Office SharePoint Server 2007' in the list, then MOSS 2007 has been installed.
If you see only 'Microsoft Windows SharePoint Services' in the list (and not 'Microsoft Office SharePoint Server 2007') then you only have WSS 3.0 installed.