What is the roll of FII (Foreign Instituional Investor) in our stock market.?

As recent uptrend of the sensex & Nifty , it is said that these are due to FII ( Foreign Institunal investor) who have been buying the shares of the comapanies since mid-august 2007. My queries are what is the Rule Governs for investmentment by FII in our stock market. Why & how they are taking prominent position in our stock market. What is the Pro & Cons of these trend.Please clarify.

They have deep pockets and long-term investment plan, more structured approach. So they invest heavily and get the sensex more and more higher. But market for retail investers or Small investers have become very dangerous, due to FII's heavy investments.

they are playing with economy.when they loose money in some other countries they take that money and invest here,when they are going to loose here they will withdraw from here also

FIIs are mostly Mutual Funds and Pension Funds.They invest in emeging economies to reap high returns.The role of FIIs is not that much in Foregin Markets.But in India,the stock markets they are controlling the Sensex and Nifty.In coutries like India due to absense of large number individual(public investors) and the market is an oligoply,with few participants like banks,insurance cos,mutual funds andFIIs the index is inflated and does not show correct fundamentals of scrips/markets.FIIs rig the market and make profit and repatriate at the cost of local inveators.Too much influence of FIIs in stock market is undesirable,