looks like a map turtle of some kind to me... the keel on the carapace and the serrated margin toward the back rule out the red-eared slider. i could be off about the map turtle part -- my knowledge of species outside of Vermont is meager (but growing)

in terms of food, a mix of reptomin, lettuce, fruits, and nightcrawlers would make up a fairly well-balanced diet. the exact proportions evade my memory at the moment but i can get back to you on that. how big is the little bugger anyway?