Tempature for Turtles Water?

Hi,
I hope someone can help me. I bought a turtle, don't know what kind it is.... it's small and very cute. I don't know much at all about them except for the house I bought for would not due. So I bought it a fish tank because that was what the pet store keeps them in. I know to have a ledge for my turtle so it can get out of the water, I have her a nice tank with ledges and of course I bought a heater because I know they NEED heat.... BUT..... Does anybody know what the tempature should be????
I have her tank all set up and it is warming up for her... she's really gonna love it! Just waiting for it to get warm enough for her.
I'd sure appreciate any advice. :)

I have had my turtle Georgie for 18 years now. The pet store toally gave me the wrong information but experience teaches. So here are some tips. First the bigger the tank the more your turtle will grow. I started with a 10 Gallon and now she is in a 55 gallon. You have the tank set up right with ways for to get out of the water. You also got a heater which is excellant. Only other things you need are a thermometer strip (very cheap) to place on outside of tank. Which should read 88 degrees for right temp. Also get a light which can sit atop the tank use Day Glow 100w lights. This helps warm tank and turtles like to bask this light creates natural sunlight.
Hope it helps Ashia