You will need one DP cable, and two DVI cables. The 5870 has one DP, one HDMI and 2 DVI connectors.
I actually may be selling my U2410's, so you could pick them up at a bit of a discount. I've had them about four months, and they have a three year warranty. May be a week or two before I can turn them. When are you looking to buy? I've got original packaging, sound bars (I set them up for surround with left, right and center) and cables from Monoprice.
Also, I'm a big fan of multi-monitor stands. You can see a couple of reviews
here. There is a WSGF coupon for 10% of the Ergotech mount I reviewed. The 2410's are great. They are big and heavy, so you'll want a solid stand.
Also, the 5870 works great. You can see some benchmarks I've run by clicking the "Benchmark" link in the left nav. I'm finishing up a whole set of benchmarks all the way from the 5870 to the 5450. I'm testing nine games total, from 1680x1050 all the way through 5760x1200.
The 2410's work great. I just have the opportunity to get six matching panels to test the Eyefinity6, and I think I'm going to do that.