If you are speaking about the boxed FSX Deluxe Edition with the Acceleration Pack, you just have to run the DVDs. Theoretically! Because, like for FS generally, a set of tweaks and tricks may prove useful (check on my flightsim site for details: http://flightlessons.6te.net/tutwork.htm#reinsta, and also possibly the beginning of that page)
On the other hand, as dumb as it seems, a good installation first requires clean DVDs. Which means just cleaning them, will ease the installation process