My advice: find a certified financial adviser. Absolutely no offense meant (gotta start somewhere), but your question indicates you don't have a handle on how to handle the risk that you take on with investing, or what your goals for investing are. In general, the conventional wisdom is that the sooner you want to use your money, the less risky you want to be. 6 months to two years? That's CD or HSBCdirect account territory.
One book I would recommend that you get is "Personal Financial Planning", by G. Victor Hallman. I took his class at Wharton - he's not that interesting a professor, but his book is full of great information on coming up with a cohesive strategy on how to manage your money. I also recommend "Stocks for the Long Run", by Jeremy Siegel.
Investment isn't just a short-term isolated game. Your investment strategy should vary depending on your goals and the level of risk that you're willing to tolerate. If you need that money in two years to pay bills or buy a house or something important like that, DO NOT put it in the stock market, because you'll be up a creek without a paddle if the market turns on you. Play in the stock market with money that you won't be needing to use for routine expenses for quite a long time. Basically, before you invest, ask yourself: What do I want to use this money for? When am I going to need this money? Will I be able to sleep at night if the market has a few bad days?