it "should" have installed as part of the download but could have suffered a glitch on the way down.
Once installed, it should be in the Applications folder.
Did you look in both the application folders, the one in your home folder and the one you see when you open the hard drive?
I cannot find it in aps. its been download iOS lion I download it at the apple store after lion was install. How can I get the tap on the touchpad back ? thanks