[OSM-newbies] Large Data Imports from websites like USGS

[Evan]

Hi all, 
I was wondering how you would import large areas of data like has been done in New Jersey and Georgia (U.S.) instead of doing it manually using tags like natural=wood, landuse=farmland, etc.  Is there a website where you can download data from and use an editor like JOSM to process the data and upload to OSM.  
I'm kind-of new to OSM (I don't know any of the really advanced things like this yet), so I would love to learn more about more advanced mapping and any help would be greatly appreciated.

 Thanks!!