Actually - the sport package adds different wheels/tires/suspension.

The ride is considerably firmer, and on some years it includes
the sport seats (also firmer than the comfort seats) with the
adjustable knee bolster. It may also (again, year dependent)
include the M series 3 spoke steering wheel (which means it
can't be a heated steering wheel - the M wheels didn't offer
this..)

The premium package depends on the year - BMW adds things to it as the
model ages. It usually includes things like the heated seats, premium
wood, leather interior, etc - things that pretty much are standard
on any BMW imported to the USA. I doubt if you can find a 5 series
in the US without it. Later premium packages included automatic
headlights/wipers and a few other goodies I don't recall offhand.

BTW - a '99 528it (touring=wagon) is an E39 series, not an E38. E38
was the previous 7 series, a quite different beast.

HTH