Avinash The quran makes no such statements abt killing someone who doesn't believe in him
the verses u probably read about were referring to those kafirs (non-muslims) who were waging a war against muslims during that era, quranic verses have to be read in the right context ..
and for the muslims who kill ppl who don't believe in allah, well i can't figure out what prompts them to be so cruel and sametime imagine that killing a non-muslim would guarantee him a place in heaven........highly ridiculous to believe that a religious book would approve of such an act, the world would have been doomed 1400yrs ago if all muslims believed that..