Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\Msi.Package\shell\runas]
@="Install &as"

[HKEY_CLASSES_ROOT\Msi.Package\shell\runas\command]
@="msiexec /i \"%1\""

http://www.windowsnetworking.com/kbase/WindowsTips/WindowsXP/RegistryTips/Security/InstallingMSIPackageswithElevatedPrivileges.html

RunAs is a great way of temporarily elevating your privileges to admin level when you are logged on as an ordinary user. However, while you can right-click on .exe files and select Run As from the shortcut menu, this doesn't work with Windows Installer (.msi) packages. 

Here's a workaround that makes this possible. 

Credit for this trick goes to: http://www.windowsnetworking.com/kbase/WindowsTips/WindowsXP/RegistryTips/Security/InstallingMSIPackageswithElevatedPrivileges.html

MSI Right-click Context Menu: Install As (other user or administrator)

Windows Registry