Maxed out the core clock @ 960MHz and the best it can do is 145Mh/sec...
Because you're using the newest AMD APP, which is probably 2.7. 2.7 and 2.6 blow HORRIBLY for anything that doesn't absolutely require it (see radeon 7000 series). Use 2.1, 2.4, or 2.5 (I recommend 2.1, but you won't be able to use it on that driver. I think the newest driver that supports 2.1 is 12.3, but you should still probably use 11.12 or 12.1).
Uninstall the entire thing, delete amdocl64.dll, amdoclcl64.dll, and OpenCL.dll from C:\windows\system32 and amdocl.dll, amdoclcl.dll, and OpenCL.dll from C:\windows\SysWOW64. For whatever reason, amd app and opencl aren't properly uninstalled when you uninstall the driver.
Download and install 11.12. Link is here.
http://support.amd.com/us/gpudownload/windows/previous/11/Pages/radeon.aspx?os=Windows%20Vista%20-%2064-Bit%20Edition&rev=11.12Driver is mandatory as well as the amd app. Catalyst control center not necessary at all. Reboot for funsies.
Recommended to install SDK 2.1 as well, but you only need to install ONE THING from the package. Unfortunately I can't find a link on amd's site. You can either download and install the only package you need from my dropbox here:
https://dl.dropbox.com/u/9768004/ATIStreamSDK_dev.msi or you can google for ati-stream-sdk-v2.1-vista-win7-64.exe and extract contents and navigate to Packages\Apps\ATIStreamSDK_Dev_win764a\ATIStreamSDK_dev.msi. This will create a second openCL platform called "ATI Stream" that many have found a little faster than 2.4/2.5 (I believe 2.5 comes with driver 11.12). Note: Most miners will NOT find the ATI Stream opencl platform unless AMD APP is also installed. Also, ATI Stream -must- be installed
after AMD APP is installed.
After you install ATI Stream, you should be able to mine at proper speeds. You should get something like 195 mhash on a stock speed 6770. 1GHz would push about 230 mhash. Make sure you select the proper platform with your miners settings. With CGminer or BFGMiner, this is with the "gpu-platform" argument, followed by a number. 0 is the first platform, 1 is the second platform, etc.
Make sure you are using the phatk (or phatk2 if you are using phoenix) kernel, BFI_INT if using something other than CGMiner/BFGMiner, worksize of 128, and vectors enabled or set to 2 (depending on miner). Also it is recommended to set memory low, usually in the area of 160-190MHz depending on core speeds; the optimum ratio is close to a 5:1 core speed to memory speed. It takes some fiddling around, but you will see much lower temperatures and likely higher mhash than stock memory speeds.