Lets see if I could help here.
The need of a cycled tank before live stock.
Ammonia and nitrite will kill fish,so we try to eliminate them. Using most chemicals only take care of the issue temperarily and therefore, we look for a natural long term way to handle it-a properly cycled tank. In a properly cycled tank, the bacteria that takes out ammonia will be of utmost important, therefore, we have to promote the growth of them. These bacteria will turn ammonia into nitrite. However,when nitrite is high, fish also die. Therefore, we need another way to take out the nitrite. There is a temperary fix - add a little slat to the water to negate the effect of nitrite in the blood stream of fish. However, the long term solution is still bacteria again but this time another kind. These 2nd kind of bacteria cannot live in high ammonia environment so they thrive only when ammonia is zero. All of what I said above provide you the thoery behind cycling tank and that you should realized, by now, the key to sucessfully cycle a tank is timing and the procedures-the timing and procedure of what you put in the tank. There is a link in About.com describing how to properly cycle a fresh water tank.
Suggestion at this point:
1)Have someone with an established, diease free tank to hold your fish.
2)Since your ammonia is zero, use some salt to negate the effect of the nitrite in your fish to save their lifes.
3)If you have to return them to a LFS, make sure the tank is diease free. Most LFS' tanks have diease.