I bought the quakecon pack and got new vegas and the DLC. I just finished the regular game but i dont know how to load the DLC. When i go from the main menu to downloadable content i see the three DLC packs there but when i click on them or hit enter they dont do anything. How do i get the dlc to load up?

When playing the game you'll get messages that pop up on screen telling you about the DLC. Normally it's a radio signal and a location you need to head to. Once you complete the game, that's it, you can't go back so load a previous save before

Oh ok. So i have loaded up my save prior to hoover dam. Where do i need to go though? I dont see anything on my map? How do i know if i am playing something associated with the DLC and not just the main game?

If you've got the DLC installed then a new quest should be added to your Pip-boy with directions on how to start the DLC.