Open it and drag the application from it into the applications folder. That's all Folks. finished. done.
And the amazing thing is even Microsoft does this. Pop in the Office ver:X CD, and drag and drop a "Microsoft Office" folder to the Applications folder (and probably either using the easially customizable toolbar, or springloaded folders to do so). Install is complete.

Tons of minor little things like this made me realise I am truly happier using an OS X based machine for anything beyond gaming. And while Longhorn might copy Quartz Extreme, Apple is putting it to good use with features like Exposé. I still am suprised at times that I switched, but now I share the same enthusiasm about OS X as I do with my empeg.