Most people will tell you that day trading is a money risk that's not really worth the effort. If it's a risk you're considering, take a look at TradingSim first, a flash-based site that simulates day trading without the money risk.
The fact is, day trading is pretty similar to gambling, inasmuch as for most people, over time, the House always wins. It's not an endeavor we'd recommend as a safe money move, but if you think you're the exception, consider trying your hand without involving cash at TradingSim. Then, even if you do well with your fake money over there, we'd still remind you to move forward into actual day trading at your own risk.
Ever dabbled in day trading yourself? Used similar tools? Have strongly-worded warnings against it? Let's hear your thoughts in the comments.