I've just committed the first patch to the git tree that should enable 79xx cards to work properly under cgminer (delete any dodgy .bins created before this attempt). I have no idea if it performs even remotely well, but in theory at least, it won't behave stupidly as the current version does. If someone does run it, could you please dump the output of -D -T the first time you run it? Also it may be worth starting it with -v 1, and/or experiment with various combinations of -v and -w (default being -v 2 -w 128 if you set nothing).