SWEET!!! Finally something I'm knowledgeable in :p Do you have pics? They're most likely Red Earred Sliders. They're going to need a big tank - do you know what size they are, in inches? Getting something 150 gallons +. You can get preformed ponds at home improvement stores for pretty cheap, with high gallonage. Also, stock tanks are cheap and high gallonage. As for cleaning, it is tough to keep their water clean since they eat in it. One way to reduce waste is to feed in a seperate container, and let them chill so they will poop in it too. You can make your own canister filter out of a rubbermaid tank and a pump. It's really easy, and effective. They'll need a dock, which you can buy/make, a heat lamp, probably a water heater since it's cold in your area, and UVB.
Summary:
Tank - 150 galon +, stock tank or preformed pond (or custom indoor pond)
Filter - Rubbermaid tub, pond pump - something with about 3x or more GPH then what your tank holds, tubing. For the filter element, people do multi layers - I've heard of Nylon, air conditioner filters, and some sort of biofilter like lava rocks. You can buy a DIY pond filter kit, and get a pump - I'm running one, and I added lava rocks to it.
Light - clamp lamps, for the heat source use a Turtle Tuff bulb. They're water proof. I used non-turtle specific ones, and they burned out real quickly. Reptisun UVB bulbs are the standard. Mine get sunlight from a window above the pond.
Docks - we use a Zoomed large dock, and stuck shower tube through the holes and attached it to a pump at the bottom to keep it in place.
Diet - some people are super against feeding retail food. I feed a little Reptomin every night, and supplement with spinach, carrots (to prevent ear infections), live fish, and occasionally little treat shrimp/krill. Make sure the retail brand food has D3 injected - that along with UVB give them the ability to process calcium. You need to dust their food and feed them calcium once a week.
Heat Source - you'll probably need one. I don't use one yet (live in Soutern CA, lows of 60

). When you get one, make sure it is un-shatterable, or comes with a shield.
Austins Turtle Page is a good source for info and care sheets. Here's some pics of a couple of mine:

Pastel Red Earred Slider - got at Pomono Show for an awesome deal, she has some shell damage so we were glad to get her away from the shop.

Pancake - Western Painted Turtle. These guys are waaay more outgoing then the Red Earred, Pancake lets me pet his head, haha. He grabs the live fish, and swims with them in his mouth for a while before he eats it

Pancake and Butterface (long story short - rescued her from being dumped in a lake, and she had a major ear infection. Big bumps on each side. Not being able to remember her name at the time - it was Nalu - I renamed her Butterface) basking in our indoor 35g pond setup. You can see the canister filter in the background, my cat Ono, the clamp lamp with Turtle Tuff bulb, dock, and if you look real closely beneath the kitty, the pump. In the background, you can see our 20g long setup for our two hatchlings.
If you have anymore questions, I'll do my best to answer it. Turtle keeping is challenging, but super rewarding. Watching them is awesome, they're really great animals.