How much money to invest?

Any amount as long as you can sleep at night.

According to my point of view Stock market is the best plae to invest money. Doing intraday trading can grab a good amount of money in short time period. A frined of mine started intraday trading with $500. And now he has made approx $1000 in a month. He trades through an automated trading system, which helped him to earn a good amount of income.

You should start with whatever you can afford to put away.
Are you going to be making regular contributions on a monthly basis?
Consider mutual funds that you can add to without having to pay fees. Some funds will let you start below their minimum requirements if you set up a regular contribution.
Try looking at investment firms like Fidelity and Vanguard. Vanguard tends to have lower fees, but Fidelity tends to have lower minimums.
Consider a broad based fund like an S&P 500 fund to get started.
Call them up and spend some time with them on the phone. They will ask you questions about your saving goals and tolerance for risk and they will be able to help direct you to the right funds. Go talk to some real professionals. You will get better answers than what you would get on Yahoo! Answers.

Rare collectible thimbles. I'd start with a million dollars.