Linux / Widows dual booting screws up bios time

Don't know if anyone else has ever had this problem. I seem to be in this endless loop of out of time sync.

If i load Linux it will be off by 4 hours, and then i notice the BIOS time will also be off by 4hours, then i load windows xp and its ahead 4 hour but usually before i chn manually change it, it switch to the right time but again BIOS has been changed again..

Same damn things happening to my Blackberry, i live in -5GMT timezone, yet no matter how many times i sync it with my computer or the networks time its always an hour ahead (there no daylight savings time option on the pearl that i have yet to find)

The only thing I can suggest is replacing the big circular battery on the motherboard. That's what keeps track of the time. Sounds like that's what's causing the problem, but who knows...