All Christians agree that Jesus was immaculately concepted. What the Catholics teach is that Mary was also and that she was sinless. This is where they are off base and it does not teach that any where in scripture. But Jesus was born of a virgin that is not in dispute. (not by any true believer at least)
This verse is the basis of the idea of the the sinlessness of the Theotokos. I'm not too familiar with the Orthodox POV regarding the Theotokos in this regard. I don't think they necessarily call her sinless, but I don't think they ever had it questioned really, it's just assumed. I'm sure Ryan1976 will be glad to clarify things.