You need to play Broken Steel before you complete the main story, but the rest can be played whenever you want. The locations get added to your Pipboy.
Ohh I would certainly not say no to that. Is the DLC best played after you finish the main game?
I have the dlc disc if you ever want a lend, if memory serves you only need to download onto your hard drive...and you have all the lovely dlc
I will pm you.
"Duffman the grey is thrusting in the direction of the problem! Oh, yeah!"