C# Check if run as administrator

Possible Duplicate:
Check if the current user is administrator

I need to test if the application (written in C#, running os Windows XP/Vista/7) is running as administrator (as in right-click .exe -> Run as Administrator, or Run as Administrator in the Compability tab under Properties).

I have googled and searched StackOverflow but i can not find a working solution.

My last attempt was this:

if ((new WindowsPrincipal(WindowsIdentity.GetCurrent()))
         .IsInRole(WindowsBuiltInRole.Administrator))
{
    ...
}