Are the new iMacs preloaded with OSS leopard?

No.

Leopard won't be released until october.

Yeah, that's a bitch. (can I say that?) I waited 6 months to buy a new mac because I was promised it would be out in spring. Finally I couldn't wait and bought in June. Now it's October!?! The first promise was in the previous December.

When it finally comes out, Leopard will cost $129.

It is alleged to be released in Oct., but I wouldn't buy the new iMac (cheaper, BTW, but no 17" screen any longer) until the Leopard is actually released. Look at Vista...(or avert yr eyes, depending on POV.)