momentary freezes issue

[zhangke7312]

When I play IL-2/Pacific Fighters, I get a momentary BIG drop in frame rate in very 5-10 seconds.
With fps data displayed in IL-2, it will be 70 fps, then suddenly drop to around 3-20 fps, then go right back up. It looks like freeze a little time.

This NOT occurs only when it plays a radio speech file. It does occur in everytime, even I fly a single plane on the sea! I have done various tweaks to my system, such as disabling unneeded services, turning off hard disk last-access update, page file on another partition or disabled, etc. But this issue is stil there!
Anyone can tell you, how to slove it?

My spec:
desktop Intel Q6600
Nvidia Geforce 8800GT
2 gig ram
Window VISTA