To disable User Access Control:
C:\Windows\System32\cmd.exe /k %windir%\System32\reg.exe ADD HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System /v EnableLUA /t REG_DWORD /d 0 /f
To enable it:
C:\Windows\System32\cmd.exe /k %windir%\System32\reg.exe ADD HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System /v EnableLUA /t REG_DWORD /d 1 /f
Both of these require a reboot. If you would like to disable Admin approval for the built-in administrator account to get rid of UAC, you can use Local Security Policy (LSA):
- Start > Run, Type: secpol.msc
- Scroll down to Local Policies > Security Options
- Double click "User Account Control: Admins Approval Mode for the Built-in Administrator Account" and select "Disabled"
User Account Control is similar to Ubuntu's root access. In Ubuntu, you run everything as a normal user. When you need to be super user (root) you use sudo in the command line. In GUI, it asks you for your password. Vista can imitate the same behaviour. By default, instead of asking you for your password, it merely tells you that the action you are taking requires elevated privilage (administrator context) and asks you to confirm it.
The purpose is that if an application is trying to do something without you knowing it, it would be stopped. So, if you are changing these settings, you may not be doing yourself a favor.