Yeah, I gots a new card - first ATI card I've used. I'll update the rig sig in a bit.
First appeared after I installed the display driver I think.
Bought the card, uninstalled nvidia display drivers, and deleted related files in explorer and registry entries in CCleaner. Also removed all MS kb[number] uninstaller entries while I was there. Switched off and swapped cards, booted and downloaded latest official Catalyst drivers (...was this wise?) instead of using the driver CD. Installed display driver only.
d/led and installed ATI Tray Tools via guru3d. Had Rivatuner already, uninstalled that and removed remnants with CCleaner. Installed Asus GamerOSD software only - not any of the other stuff on the CD.
ATI Tray Tools asked to disable the 'ATI hotkey poller' service on starting and I told it to do this every time it runs. Played with some display settings and tried the low level OC settings.
Actual problem is any changes to the clock settings or auto testing result in a bsod that mentions the Catalyst driver file ati2mtag.sys. idk whether to change it first or try another utility.