Well sheiit, you drive a 2002 and I believe that after 2001 the skirts that came with the S2 became standard. I drive an S2 and the mounting hardware that came factory for the factory side skirts worked perfectly for the Roush side skirts. IIRC, all I had to do was drill a few holes into the side skirt and use the factory mounting hardware. Nothing major at all, for realz.
Dip down and take a peak under your car and see how your current side skirts are mounted, then get an idea of what has to be done to mount them. Also, run a line of 3M automotive emblem adhesive along the edge to help secure it even more.
If you're curious, look at the last photo in my gallery and you'll see what my side skirts used to look like, then look at the more current photos. It was a sinch [thumb]