I had the problem with my clocks going out of sync by an hour. Here's what I did to correct my problem.
1. First fire up Registry Editor by typing regedit.exe in Windows 7/Vista Search Bar. If you get a UAC prompt, hit 'Yes'
2. Now Navigate to this key, to do so simply keep on double clicking the folders till you come across toHKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\TimeZoneInformation
3. Right click on the empty space right below TimeZoneKeyName and create a new DWORD(32-bit). On 32-bit versions of Windows 7/Vista, you will only see DWORD
4. Rename the new DWORD as RealTimeIsUniversal (without quotes and its case-sensitive)
5. Double click on the new DWORD and change its value data 0″ (thats a zero) to 1″ (one). Its in hexadecimal
Save it all. Reboot to Mac OS X, set the time properly and now boot back to Windows. You should notice the time should be the same as it was set in OS X.