Daniel (and everyone): There are Zuiko lenses for the Olympus Ace, Pen F/FT and FTL (as mentioned above). Those lenses will NOT fit the OM series, at least not without an adpter for the Pen or FTL lenses. FWIW, I doubt you could use an Ace lens on an OM without serious surgery or a custom-made adapter; the Ace was a rangefinder, hence the lens registraton distance was much closer, so even if you could physically get it on the body the rear element might impinge on the mirror or at the very least you could not focus at infinity.
Olympus Zuiko lenses that fit the OM system directly are labeled "OM-SYSTEM " or "M-SYSTEM". The OM-1 was originally the M-1 , but Olympus changed the name as Leica objected to the use of the "M" designation due to Leica's trademark. The M in OM stands for Maitani, the leader designer/engineer of the OM system.
haris: The Zuiko 28/2.8 and 28/3.5 are both very good lenses. I don't see much difference between them except for the speed. The best short telephoto value is the 100/2.8, which is a great lens for the money. The 100/2 is reportedly wonderful, though I have never owned one. The 90/2 Macro is superb and coveted by many, but it is expensive. If you ever find one and can afford it, BUY IT.
The 50/1.4 is worth having, especially if you get one with a serial number of 1,100,000 or higher; those were the best version of that lens. My 50/1.4 is in the 6xx,xxx range, and it is very good.
Another very good lens, especially for the money is the 35/2.8.
All-in-all, Zuiko lenses are very good to superb. I like my 21/2 as much as I liked my Leica 21/3.4 Super Angulon. They are different in character, but the Zuiko is as good in many respects, especially at closer focus. I have not owned one, but many feel the Zuiko 50/1.2 is close to some of the 50mm Summilux versions.
Don't let anyone pooh-pooh Zuiko lenses. There are certain Nikon, Pentax, Minolta, Canon or other lenses that one may feel are "better" in a particular formulation, but "better" is a very subjective term.
Earl
Zuikoholic