And start with an integrated GPU like batuchka suggested, should it prove to be slower than you need, look into a HD5400, 5500 or 5600 series of video cards, you pay a lot for support and special drivers (used for CAD and other design chores) when you get a workstation card, the actual hardware is more or less the same as used in "gaming" cards.
like lthdk and batuchka said, u dont need a workstation card to use for streaming stocks/index and so on. But in order to run 2 High resolution monitors, u might wanna invest in what batuchka says (if i am reading correctly, i believe he is advising you to buy a mbob with hybrid crossfire with an 880g chipset and buy a 5450 along with it - set up hybrid CsfireX) or crossfire two 5570 with your current mobo.
Link for 5570 - http://www.newegg.com/Product/Product.aspx?Item=N82E168...
overall, it might be about the price of a 5770, so you can pick up one of those two
Sry for the long post, but i do not believe that intergrated gpus can run two monitors at around 2560x1600, the two 5570/single 5770 might be overkill yes, but it will (to the best of my knowledge/if i am wrong, please correct me) that is cheaper than the workstation cards. The workstation cards are tailor amde for engineering programs (like cad), video programs and so on.
Video Card: http://www.newegg.ca/Product/Product.aspx?Item=N82E16814121354 $81-30MIR = $51
will run 2 high res monitors smoothly as long as all you are doing with them is not highly graphics based. again, if it is just web browser, os stuff, office apps, it will be absolutely smooth. im assuming one of your monitors have an hdmi input
TOTAL = $454. Even less if you can get your OS elsewhere, from friends or what not. if you can get your hands on an xp copy that would make your experience even more lagless, just because its lighter. although the dual monitor support may not be as great
Im using a C2D 7400 at work with some low end asus board, and i have absolutely NO lag at all when im doing anything (given all i need to do is all browser based and office apps) the gpu should be able to handle anything you need for day trading because nothing should be 3d, or heavily rendered. if you're really that worried, go for a gt 250.