My girlfriend has a res too. She is slowly getting around to letting me buy her all the stuff it needs.
Right now the most important thing to get will be the dock. If the turtle spends all of its time in the water its shell will eventually begin to rot. It will start with pinkish patches on the bottom of the shell.
http://www.austinsturtlepage.com/Car...ear_slider.htm
That page will give you all the basic information you will need to know. The people on the turtle forum are very helpful and can answer any other questions you have.