It appears that there is not a great deal of difference, except for the extra megapixels, size of the LCD and the type of batteries.
I have not seen any reviews of the SP-500 yet.
Here is a comparison:
Any thoughts on which to buy............my brother loves his C-770 and I was going to get one until I read about the SP-500. I really don't need a 6 megapixel camera but if it's a better camera the additional $60 +- would be worth it. I like the AA batteries that the SP-500 operates on vs the rechargeable type. I also like the 10 power zoom of both cameras.