As you put the lightweight dryer on the heavy washer, it's not a big problem. We put a special retractable tray part between the two so that you have a place to put your basket when emptying the dryer. I don't know if such a thing is available where you live and how it is called.
http://www.amazon.de/Verbindungsrahmen-mit-Arbeitsplatte-Waschmaschine-Trockner/dp/B001BYJ73A/ref=pd_sxp_grid_i_1_0

Make sure you have at least 2 strong people lifting the machine.

Many (all?) of the stackable models require a "stacking kit" to attach the dryer to the washer. Contact the manufacturer to get the appropriate parts and make sure you follow all of the installation instructions. You wouldn't want the dryer to "walk" off the top of the washer and on to the floor...