I would try to set in the Flag Box "-v 2 -w 256" or even "-v 4 -w 236".
For further help you should check if anything graphical runs in background (video,music etc playing). Very bad on GPU usuage is the always loved Flash(tm) plugin of your browser.
Open your Task Manager and check for CPU Load.
otherwise i can suggest using cgminer (find it on
http://ck.kolivas.org/apps/cgminer)
there is a very easy to understand manual for configurating. Another big advantage is the very well output of the app. So Error Detection is easier.
use --debug for a lot of output.
my TipBox:): 1Nrs2jTZddhhZEbawR27ambdiz7FnvdBH9
With "-v 2 -w 256" my hash rate has doubled, but 700-800 khash/s stil seems low?
The CPU load is 100% and when checking with GPU-Z the GPU load is 44-5%. So it would seem that it is running on the CPU rather than the GPU despite i selected device "[0-0] Tahiti"?
I would really prefer using GUIMiner, but I will take a look at cgminer.