The S has
- a complete different suspension incl. sway bars; spring rates are different, because of the weight dif
- an additional oil cooler in the front incl. lines
Further differences
- water and ac condensers are the same
- wiring harness might be different because of a different ecu
For more details, just take a look in the parts catalogue and compare yourself:
http://www.porsche.com/all/media/pdf/originalparts/usa/986_USA_KATALOG.pdf
Regards, Markus