EXACT same issue here.  Windows XP SP2, ATI 5770 vid card.  Latest Catalyst drivers, installed ATI Stream and all accompanying files.  Still "No OpenCL support" with GuiMiner

Edit- May have at least partially solved the issue.  By rolling back to driver version 10.6 and ATI Stream version 2.1 I now have access to the card in OpenCL.  The card shows up as "Juniper" but I believe that is the accurate name of the chipset.

Averaging 176 M/Hash with this software setup and the -v -256 tags.  No clock changes of yet.  Will OC later.


Another Edit- Seem to get better results at -128.  Clocked at 925mhz Core and 600mhz Memory (MSI Afterburner wouldnt go lower)

Clocking core to 960mzh seemed to make little to no difference over 925 (Afterburner would not go higher)..
Raising memory clocks made little difference.