Swap Plays For Draws and Play X with fewer than X cards on hand
This is answered in the Fluxx FAQ:
http://faq.looneylabs.com/question/272


  if you have 3 plays left, you get to draw 3 cards, even if you only have 1 card left in your hand. Of course, now you’ve used up your plays, so you can’t play any of those cards on the current turn.