http://www.redearslider.com/forum/viewtopic.php?t=8864
Here is a set up showing the lights you'll need. The UVA provides heat, and the UVB provides UVB essential for good turtle metabolism. They should both be near the basking dock. You may want to skip on all the stones this person used as that adds a lot of space for dirt to get trapped in the tank.
When you go to petland you'll need to pick up a UVB light (compact or tube... depending on how you want to set it up). I personally recommend the reptisun 5.0 over the 10.0 because a couple of people have had trouble with the 10.0 causing irritation to their turtle's eyes. You'll also need to pick up a basking dock , a thermometer (digital not glass, because turtles can break the glass ones), and a tank heater. If you don't have one already you'll need a filter that is rated 2-3x the size of the tank you'll be using. So if you're using a 20g tank you should look for a filter for a tank that is 40-60 gallons. If you buy a less powerful filter it just won't hold up against how dirty a turtle can make the water and you'll be dealing with very frequent water changes.
Also, if possible, start with the LARGEST tank you can afford, it will save you a lot of time and money in the future in the way of upgrading. Even something as small as a 29 gallon tank is a better start than a 10 or 20 gallon, you can always build an above tank basking area in the future to increase the tank's use.
also: I forgot to mention, don't use tiny stones in the set up because turtles WILL eat anything that can fit in their mouths, and this can lead to impaction and death.