What the heck is fallout vegas? There coming out with fallout 4? So what is it? A small miny Fallout 3 game in vegas?

It is a side game like fallout tactics. Or what fallout tactics 2 was going to be.

It will be canon like the other fallout games. New Vegas will be a full game not a mini game or a DLC.

Basically what Styles said. Fallout: New Vegas is being developed by Obsidian; it's a spin-off of the main series, and is going to be based on Fallout 3's architecture - making use of the GECK and likely re-using a lot of the same assets. Fallout 4 is the (currently hypothetical, though highly probable) "next full sequel" in the series, which would be developed by Bethesda. There's so far been nothing announced about Fallout 4, although it's gnerally accepted that Bethesda bought the Fallout franchise with the intent of making more than one game, and a safe bet that they'll be working on making another game at some point in the future.

Think GTA: Vice City, or San Andreas, and you're all the way there.

Check that first forum in the forum list...

Heh-heh. Where have you been, stranger? This has only been news since last April.

All the information is in the http://www.gamesas.com/bgsforums/index.php?showforum=78.