Well, technically ick is always present in a tank, unless you treat it to the point where it's killed off, but generally then the fish would die to. Usually, healthy fish can fight off the disease with no problems unless something is messing with their immune system for some reason.
SOOO...
the problem with it appearing in your fish means that the fish were stressed out by something that's changed (I'm guessing that the addition of the new fish stressed them) or by poor water quality. I'm not sure in this case which it would be, but if you get them treatment they should be fine. But make sure you get it first thing tomorrow morning!
guppyman -
if your fish are showing any signs of white spots, you should treat them right away. Pick up some sort of ick treatment - maracide if you can find it, but pretty much any ick meds will work.
BOTH OF YOU - also make sure you've got really good aeration in your tanks while you medicate. Meds take oxygen out of the water and your fish can suffocate. Also, if you can - raise the temp up to 82 degrees. That will speed up the cycle of getting rid of the ick.
Good luck!
OH! ALSO...
if you have carbon in your filters, you'll need to take the carbon out while you medicate or it will render the meds useless!!!