how do i change admin privileges in Vista????

Hi all I am having a problem installing heathrow 2008....and I am sure its that nasty windows vists account settings..when I right click on the setup.exe file to bring up properties I then click on the compatibility tab....the box I NEED to check, I think, is the ''run as administrator'' box but it won't let me..its greyed out...how do i check this box..I have full admin rights right now which I thought allows me to do anything?? please, if anyonme can help me it would be much appreciated!