if you want to buy tonight you might be too late on the decision.  Dwolla takes about 2-3 biz days to clear your account, then another 2-3 biz days to post the funds from your account. Sending that over to TH or Gox might take another day?

I personally went Dwolla - > Exchange, but like I mentioned it takes time to fund it. If you haven't signed up on Tradehill the link in my sig will take you to that.

Good Luck & Welcome!