Belief in the Old Testement precudes belief in the New Testement or Koran

Sinces my opponent numbered his arguements, I shall number my responses according to his for easy refernce to which point I am addressing. 1. My opponent quotes Isaiah to prove the Torah predicts a Mohommed bringing a new law. I have three points of contention: Firstly, although those verses speak of the messiah, they do not say they are refering to Mohommed; they can only be applied to him retroactively if you believe he was the messiah. Secondly, the word my opponent translates as "law" is, in Hebrew, "torato" or "his teachings". "His Laws" would be "tzvivato". This merely sounds like the messiah will be a great teacher, not institute laws of his own. Thirdly, this only can prove that he will institute new laws. The verse says nothing about overturning the laws of the Torah, because no one is allowed to do that. I would also point out that Isaiah himself was a prophet. If God had meant there to be an excption to His rule of no changes, surely He would of written so by the rule, not told it to a prophet hundreds of years later who himself had no authuority to make exceptions to the Torah. 2. My opponent says that Mohommed is the soles exception th the law that changers of the Law should be stoned. there is no source for this. Incidently, my opponent is right that there is no clear proof that Jesus changed the Law. However, it is pretty clears Paul did, and his gospel is part of the New Testament. 3. My opponent attempts to prove that the Torah predicts the coming of a prophet "like" Moses, who will bring a new Law. The problem is that these passages are dealing with any prophet that arose after Moses; the next verses are full of laws on how to deal with them- these are, in fact, the scriptual prophets who went under the procedures described in the next verse. In context, the word "like" means that the prophet is like Moses in the sense that he is a prophet, nothing more. At the very least, that verse is refering to a dozen Old Tesament-established prophets. Pretty shaky source for God to base his new revalation on. my opponent attempts to compare Moses and Mohommed by saying they both recieved a Law. But Moses never recieved a Law by himself! As I've stated, the Mosiac Law was given in front of 1.2 million people, as it says numerous times in Exodos. In fact, my opponent totally failed to address this point. Apparently, even Moses was not a great enough personage for God to give the Law through. God gave it in front of 1.2 million people so it would be incontravertable. How could He change His mind without duplicating the feat? This was and still is half my arguement, and I'm still waiting for an answer. 4. My opponent stated in the comments he would not use semantics in his arguement. This, I think, falls into that catagory. My opponent says that the Old Testament is true, just that what we have today is not the Old Testament. I think it is clear from my opening paragraph that I meant the Old Testament we have today. If you want to argue that Islam does not hold it is true and in its original form, all well and good; My premise is based on the fact that if you believe its true , then the Koran is invalid. Therefore, this is really irrelevant to the discussion. I look foward to my opponents response.