Sport package adds different exterior trim (shadowline/blacked-out), titanium colored vents in grill and hood, different tire & wheels (19"), sport seats (sometimes comfort seats are optional), black chrome exhaust tips, and sport tuned suspension (slightly stiffer). There might be other options, but these are the major differences from what I can remember. IMO, the options make the X look more agressive and "sporty" but the the ride is a little stiffer than with the standard 18" wheel set up.
2007 750Li Ti-Ag/Blk, sport pkg.
2006 X5 4.8is Ti-Ag/Blk, cold weather pkg., comfort seats