A month ago I searched for some tools that will generate C# classes out for my SQL database/tables. So I don\'t have to write DAL classes manually and to save a lot of time.
Unfortunately, the best SubSonic "documentation" is in the form of screencasts, but they are very easy to follow.
Quite a lot about SubSonic on Rob Conery's (original creator) blog http://blog.wekeroad.com/tags/subsonic/.
Personally found the best thing is (like Matt said) to just use it, set it up in external tools in VS, get the connection string and a few other config settings sorted, and you're just about good to go. You can get the basics down in an afternoon.
The forum is quite active http://forums.subsonicproject.com/forums/, and a good place if you get stuck.