This question has been debated enough times in various forums, I have listed some of them below, There are interesting replies.
There are some questions which are difficult to answer in simple terms, one of them being
Can God create a Stone that he cannot lift? There is no Yes or No for this answer.

http://answers.yahoo.com/question/index?qid=20080822173951AAIgRaT
http://www.amazon.com/tag/self/forum?_encoding=UTF8&cdForum=Fx3V6J6V0PF1...
http://www.thestudentroom.co.uk/showthread.php?t=695931
http://water-desert.wetpaint.com/page/Is+God+willing+to+prevent+evil%3F?...