I am supposed to learn MOSS asap because I have to work on a project that is MOSS based. I am intimidated and pressured but I think I will be able to master it soon enough and even blog my attempts and conclusions.
I am starting with a step by step workshop to grasp the basics of MOSS development. Then I have those videos that I will go through I will give myself a week or so to do it.
For as far as I know now MOSS is a web-based collaboration and document management platform from Microsoft that can be used to host web sites which can be used to access shared workspaces and documents. SharePoint functionality is exposed as web parts. These web parts are composed into web pages, which are then hosted in the SharePoint portal. SharePoint sites are actually ASP.NET applications, which are served using IIS and use a SQL Server database as data storage backend.