Whoops! Rabbit beat me to it, but I'll post my message anyway...
Go to your local Petco or the like. You will need a product called, KMR (Kitten Milk Relpacer) and a kitten nurser. It has been my experience that the opening in the nipple is too small, so you may need to widen it with an ice pick or an Xacto knife.
Room temperature should be fine, but if you refrigerate the leftovers, you can warm up the formula in the microwave. BE VERY CAREFUL about the temperature. Just a few seconds should do it.
For a kitten that age, you need at least four daily feedings at first (preferably five) then you can taper off after a couple of weeks. One thing you need to be aware of, is that at that young of an age, kittens need some external stimulus to help them evacuate. About one hour after feeding, put the kitten on some newspaper, and with a warm dampened cloth, simulate the motions made by the mother during grooming (if you get my idea&).
You may not get much at first as the kitten has not had much nourishment, but in time, youll get some results. Not the most pleasant of businesses, but unfortunately necessary. After a few weeks, the kittens bowels should kick in on their own. (Mine did right on top of a particularly obnoxious television personality as I was lifting him up one day. After I stopped laughing, I had to commend the kitten for his astute political sense.)
It is a lot of work at first, but the rewards can be well worth the effort. Hand-fed cats tend to be very loving and bond better with people than conventionally reared ones. Although I curse the &%!@#! who abandoned mine at about the same age, when all was said and done I got a gorgeous, healthy cat who lived a long, happy life. Thanks, &%!@#!
Good luck!