that is very strange. I have known things like that happening in the past but not in the manner you described. What i heard to happen is the cpu would just be detected slower and stay that way and what you needed to do in BIOS is set the FSB correctly. In the case of yours, your FSB should be 166mhz (333mhz DDR). Because yours changes all the time it could mean that your battery is running out of charge or your BIOS has a bug so look on your motherboards manufacturers site for an update, after that look for a new battery - just borrow one from a friend to see if it keeps happening.
Core 2 Duo E6400, DFI Infinity 975X/G, 2x 512mb DDR2 667mhz, Albatron 7900gt, WD 200gb SATA, Samsung DVD-RW, Silverstone ST-50EF 500w PSU.