My friend the verse that u quote was revealed in certain situation and for certain people. if u read the history of Islam u will find that in the begging Islam had many enemy mushiness of mecca, the Jews etc who have always attacked Muslims and our Prophet. Those people were specially called unbelievers and has been referred in this verse. Of-course anyone who does not believe in Allah and his final messenger is a non-believer but that verse is talking about a particular group of people who deliberately opposed Islam. There are many verses in Quran that tells us there are also Jews and Christian who could be considered as believer. Quran also states that ".. the closest in friendship you will find the Christians". As for your question that if any Muslim can help a polytheist,,, the answer is the example set by our beloved Prophet, he in his life time ensured protection and safety of the Christians and other people. So in short a Muslim should help anyone who is in need but also need to understand if the same person is anti-islam a muslim should not help him. I want to quote a verse from the Quran for you to understand it better.."If any one slew a person - unless it be for murder or for spreading mischief in the land - it would be as if he slew the whole humanity: and if any one saved a life, it would be as if he saved the whole humanity"