I wouldn't have problem with it if it only self-calibrates it upon system boot. But it also re-calibrates it whenever I wake the computer from sleep. Now this has some serious safety issue. Just the other day, my wife was sitting in my chair in front of the G25, then computer just suddenly woke up... maybe mouse was moved slightly I donno. But anyway, her necklace got caught in the wheel!!! Fortunately, the necklace broke off but if it hadn't...
This is bigger issue with G25 than any other wheel because of its large turning radius. A wheel turning half circle each direction isn't big of a deal compared to G25's 900 degree turns while auto calibration.
I contacted Logitech support about this via email and they kindly told me that there's no way to disable it and get refund for the wheel. Nice support.
I like to keep the wheel but I'd like to see Logitech address this issue. I need the way to disable the self-calibration and also a way to manually calibrate the wheel as it often mis-calibrated when computer wakes from sleep forcing me to reboot anyway.
I am not aware of any way to disable this on the Logitech side. You may want to see if you can modify your settings in Vista to keep the USB bus from powering down when the system goes to sleep. That is what is probably causing it to go through the calibration routine every time it wakes. The only other option in your case would be to disconnect the wheel when you are not using it.
BTW, unplugging and replugging the wheel should reset the calibration. You should not have to reboot to do this.