I just took home a kitten (that a friend had) who no longer has a mother. I took the kitten in because we have a mother cat which has older kittens that are still nursing, so I took him in to try and have the mother cat nurse this new kitten too. My cat took well to the kitten and was laying, cleaning, and nursing it when I first brought the kitten in. Though now it's been almost a day and she dosen't seem to want to have much to do with the new born kitten. I think this maybe because her own kittens are older now and don't need to nurse as much nor do they need her to set with them anymore.
My question is, is there anything I can do to have my cat nurse this kitten and sit with him as much as he needs to be?

There's really not a lot you can do. You may have to start hand feeding the kitten.

Unfortunately sometimes they just do not want to nurse another cats kitten.

You don't say how old the new kitten is?

You can buy kitten formula from your local pet store... it comes in either cartons of liquid or a tin of powder that you mix up yourself.

You can buy tiny bottles from pet stores or your local chemist/pharmacy.

Kittens need to be fed every few hours...

I have included a site below that tells you step-by-step how to bottle feed a new born kitten

How to Bottle-Feed a Newborn Kitten (http://cats.about.com/cs/kittencare/ht/bottlefeed.htm)