775MHz with 400 Stream Processors
Compare to a 5770 - at 850MHz with 800 Stream processors, a 5770 gets 220Mhash/s, so expect around 100Mhash/s from a 5670. Which is currently about .04 BTC a day.
This card doesn't require a PCIe power connector, but it's power rating is 65 watts, so it may or may not shut down the Dell's power supply once you fire up a Bitcoin miner after adding this card.
Actually, theres a better one. 6670. 480 SPU's @ 800MHz, single slot lower profile. http://www.newegg.com/Product/Product.aspx?Item=N82E16814131469
5670 = 400 SPU @ 775MHz
6670 = 480 SPU @ 800MHz
You're still talking about 120MH/s TOPS.