Obama on why he cannot do this. From March of last year:
http://www.youtube.com/watch?v=TfZ3kaKZoIw&feature=player_embedded
“With respect to the notion that I can just suspend deportations through executive order, that’s just not the case, because there are laws on the books that Congress has passed.” ...
“There are enough laws on the books by congress that are very clear in terms of how we have to enforce our immigration system. That for me to simply, through executive order, ignore those congressional mandates - that would not conform with my appropriate role as president.”