Ya know what refreshed? That actually touches on a fascinating subject. One of the very first evangelists I heard in my youth (I was around 16 at the time) was a convert from Islam whose burden & mission was to take the gospel to his muslim brethren. In fact, he was instrumental in my own conversion.
During one of his talks, he made the (almost astounding) claim that Islam was nothing less than a heresy of Christianity. Gotta admit, I was sceptical at the time. From my limited knowledge of both religions, I just didn't see sufficient 'cross-fertilisation' between the two to make such a connexion.
Since then, everything I have read has tended to confirm his claim. Google it for yourself if you doubt it - you might well be surprised by the results. Oh that's right, you can't. Yet more empty calories. ;-)
As for the antichrist connexion, that will hafta wait another time for a more detailed treatment, but briefly - yes, anything that purports to be a substitute for Jesus may be considered as antichrist, but the mahdi is not necessarily the antichrist:
18 Children, it is the last hour! As you have heard that antichrist is coming, so now many antichrists have come. From this we know that it is the last hour. 19 They went out from us, but they did not belong to us; for if they had belonged to us, they would have remained with us. But by going out they made it plain that none of them belongs to us.20 But you have been anointed by the Holy One, and all of you have knowledge.21 I write to you, not because you do not know the truth, but because you know it, and you know that no lie comes from the truth. 22 Who is the liar but the one who denies that Jesus is the Christ? This is the antichrist, the one who denies the Father and the Son.