How many pictures on 2 gb memory card in 8 mega pixel camera?

If you have one, your User Guide/Instruction Book/ on-screen Manual should be able to help you. For example, I have a Canon A710IS, and under "Memory Cards and Estimated Capacities" for a 512 SD memory cardit it goes from 156 for 'Large (3072x2304 pixels)' to 839 for 'Postcard (1600 x 1200 pixels)'. If you don't have a Manual, quadruple these figures and subtract 1/7th and you won't be far wrong.