It's not exactly what it's made for, but in my experience the easiest way to get money into Mt. Gox is by way of Coinbase. Setting up an account in Coinbase was easy, though actually buying bitcoins takes about a week. From there you can send coins to Mt. Gox and do your day trading there by converting to/from fiat. If your goal is just to buy bitcoins through Mt. Gox then this probably isn't the answer you're looking for, but if you want to speculate/trade, this was the easiest way I found.