1. Windows SharePoint Services (3.0) are free available with Windows Server. Microsoft Office sharePoint Server (MOSS) 2007 is licensed version. WSS 3.0 can be freely downloaded from Microsoft site.
2. MOSS 2007 is based on WSS3.0 with some additional features like Enterprise Search, Business Data Catalog(BDC), User Profile, Excel Services, Single-Sign on, additional Workflows, My site feature etc.