Windows Vista monitors the amount of available disk space and displays a warning in the taskbar when the hard disk is almost full. To disable this feature, perform the following steps:
1- Open the registry editor (Start/ type: regedit and hit Enter)
2- Navigate to [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
3- Create a new DWORD value and name it "NoLowDiskSpaceChecks" (without quotes)
4- Double-click the new value, set it to 1, and click OK.
5- Close the registry editor.
6- Log off and log back on for changes to take effect.