Consider this carefully: "When you are a long a stock, the most you can lose is the amount you paid. When you are short, you can lose unlimited money."
If you have "funny money" that you aren't afraid to lose, there are safer and more responsible ways to experiment with the market than unprotected short positions.
You may want to read about and understand some options strategies:
http://www.investopedia.com/terms/b/bearputspread.asp
http://www.investopedia.com/terms/b/bearcallspread.asp
Either one of those strategies gives you the opportunity to profit a certain amount if the stock actually goes down (the width of the spread times the quantity), while limiting your exposure to just the premium you pay for the options. Your exposure is limited because you both buy and sell puts or calls for equal amounts of the underlying, so you have no net exposure to the price of the underlying.
A general word of advice about playing the market for short term gain: big guys make money off of little guys. You may win some, but usually you are doing damn well as a small time trader if you're batting above 500 at all.