A SIM card slot located below (inside) the battery compartment in DELL. Can i use the newly launched 3G Internet services on my laptop by just inserting a 3G-enabled SIM card without the need of any other hardware?

The provision for a SIM card in your Dell laptop is given as an optional GPRS/HSPDA network connection, but it works only in certain countries and not in India as yet. Additionally, just inserting a SIM card will not help. You will need to install a WWAN card (Wireless Wide Area Network), which connects to a cellular service in conjunction with the SIM card to gain Internet connectivity. Presently, the service is not available in India. 

I would advise you to switch to a USB 3G dongle from various Internet service providers. It is relatively cheaper and will save you the trouble of investing on additional hardware. You can also use the USB dongle on other computers whenever needed.

The SIM card provision is for 3G compatibility, but it still needs additional hardware to work.