I think its Cash only. Broker is US based. Never traded Indian stocks. But from information I have we can access about 70 international markets. Including some really remote like Kenya, Botswana.
Contact Omnesys Technologies, Pvt., Ltd., www.omnesysindia.com. If you are an nri or if you have a firm that can file the appropriate papers then they will help you get started and can recommend a brokerage house. I think that this will be the least expensive way for you to trade on the NSE and will provide you with the best trading results.
They also have various strategies (like arbing stocks vs their futures) available for your use.
