UAC (User Account Control) is the most obnoxious, nagging windows that will drive you crazy and frustrate you while using Windows 7 or Vista.
One way to stop being annoyed is to disable it. However doing so will make your computer less secure. I in no way recommend anyone disable UAC, but I will provide a quick way to disable and enable via the command line.
Disable UAC
C:WindowsSystem32cmd.exe /k %windir%System32reg.exe ADD HKLMSOFTWAREMicrosoftWindowsCurrentVersionPoliciesSystem /v EnableLUA /t REG_DWORD /d 0 /f
Enable UAC
C:WindowsSystem32cmd.exe /k %windir%System32reg.exe ADD HKLMSOFTWAREMicrosoftWindowsCurrentVersionPoliciesSystem /v EnableLUA /t REG_DWORD /d 1 /f
Both require a reboot to take effect.