Can a guy with klinefelter's still have kids?

Yes: Yes. But not all men. In this situation, you would certainly need to be evaluated by a fertility specialist, possible in conjunction with a urologist to know whether it is possible for you to produce sperm and have a child.

Usually no, but....: In selected cases a functional sperm can be extracted from the testis and injected into an ovum in a process called icsi.

Sometimes: About 30% of men with klinefelters will have sperm in their testes. They are hard to find and require a microsurgical testicular dissection. Even if sperm are found that doesnt guarantee a child as the sperm have to be injected into the partners eggs (icsi). The resulting embryos should be tested for genetic abnormalities before the embryos are implanted. Few centers do this! very expensive!

Kleinfelter PG: I agree with the other answer. Let me add that many of the embryos will have an abnormal number of chromosomes, perhaps twice as many as from men without sperm extraction. If pgd is possible and there are sufficient embryos, then it may be prudent to use it. Despite all this data, the outcomes for kleinfelter men with icsi has been very good. It takes special expertise to do well.

Maybe: Some men with klinefelter's syndrome may produce enough sperm to father a child; however, they typically require a fertility specialist to perform an icsi procedure, which is a type of in vitro fertilization.