Some experts advise that cream is better than regular milk if you must give it to cats, probably because cream has less lactose than whole or skim milk. But again, a small amount of skim milk seems to be okay for your kitty, so I wouldn't worry about it. But now, there are many lactose-free milk substitutes for cats have been developed. you can get it in nearest pet shop.
source :
1. http://cats.about.com/cs/catmanagement101/f/milkokay.htm
2. http://badanimalpuns.files.wordpress.com/2009/10/cat-milk.jpg