Look for SDK 2.1. Dunno if you're using win7 x64 but the thing you want to download is ati-stream-sdk-v2.1-vista-win7-64.exe. Don't run that, but instead use something like WinRAR to extract it (or maybe if you run it, it'll extract it to C:\ati, i dunno. I just saw it wanted to install lots of garbage). Navigate to the folder it got extracted to. Navigate through the folders Packages\Apps\ATIStreamSDK_Dev_win764a and run ATIStreamSDK_dev.msi. Install it. You -may- need to reboot after installing it in order for it to be detected (Use GPU caps viewer to verify). You'll also need to restart your guiminer if GPU caps detects the second OpenCL platform called ATI Stream. You should now have a second platform available in guiminer; it'll probably look like 0-0 cypress, 0-1 cypress, 0-2 CPU, 1-0 CPU, 1-1 Cypress, 1-2 Cypress. Use 1-1 and 1-2 and that will mine on the much faster 2.1 sdk. Also assuming you have the latest phoenix + kernels instead of the one that comes with guiminer, you can use the short parameters of "-k phatk2 VECTORS AGGRESSION=12" since bfi_int and worksize are automatic and other arguments are unneeded.
gl
btw 150mhz memory may be too low. people swear on memory = 1/3 core speed, but i found absolute fastest speed occurs around 375 memory but has stability problems, so I have it on 330 memory instead.
Here's an example of a 3 card setup on Win7 x64 with guiminer, phoenix 1.7.4, phatk 2.2, 11.12 drivers, 2.1 SDK on a 5870 @ 1090/330 + 5830 @ 1040/330 + 5830 @ 1025/330.
