Contents:
1 Creating a Backup in SharePoint Designer (CMP File)
1.1 Sites Less Than 25 MB
1.2 Sites More Than 25 MB
2 Exporting a site as a Personal Web Package (FWP File)
3 Restoring a Backup using SharePoint Designer
details:
http://myhosting.com/kb/Backing_Up_a_SharePoint_Site