FSX stutters and hangs

Just wondered if any is seeing the same problems as me in FSX.1)When running Flower Power I get roughly one second pauses every 100 frames or so. This happens in windowed or full screen mode. It does not seem to happen on any other flight.2) When changing from full screen back to windowed mode (Altgr +enter) FSX often hangs, generating a) either a fault report for FSX saying that a critical error has occurred and FSX must restart or b)the system hangs and then reboots generating a serious error report with a Windows stop error (Thread stuck in driver).The system runs 3dmark2006 at 6198 with no problems.I would have said it was a hardware fault except the same thing occured with the previously fitted 7900GT.It may well be that 1) and 2) are not related.Any thoughts appreciated.