GPS based speedometer for boats project

hi sir,
i am doing a gps based speedometer project for boats using a microcontroller and i am having difficulty in finding simple way of calculating distance between two points using latitude and longitude positions and how to calculate the speed at that instant using microcontroller.
i will be very thankful if u help me ..

Yes as tippu said you can get the speed directly from the NMEA outout of the GPS.
For distance calculation you need to do some mathematics. Search google for more details.
http://www.movable-type.co.uk/scripts/latlong.html