I've tried both 12.1 and 11.12 with SDK 2.1 now and it didn't work... Still 50% load on the CPU and still fluctuating hash rates.. I'm really getting tired of this **** and I'm about to give up... And before you ask, yes I used Driver Sweeper to uninstall the drivers.
Maybe I should try a different miner? Highly doubt that'll work either though..
Try 12.2 with SDK 2.5. I always used 2.5 on my 5970s with no issues.
I'm all for switching to CGMiner, but this sounds more like a kernel issue.
As far as I can tell 2.5 isn't available for WinXP. 2.3 seems to be the newest version for XP.