I've had similar problems using Win XP. What I've found to work (mostly).
1. Keep CCC closed if you don't need it, make all changes with Afterburner
2. Do not make any speed changes while you are hashing
3. Once you make changes in Afterburner, wait a moment, then shut down Afterburner and restart it
This won't eliminate all crashes, but I've found that it eliminates most of them (at least for me). Currently set at 950 MHz core and 350 MHz memory and just under 200 Mhash/sec. 4097 shares with 31 stale (0.757%) since I last fiddled with it