whats the difference between Parallel universes and Alternate universes?[/b]
In meaning no difference.

But I say \"All parallel universes are alternate universes but all alternate universes are not parallel universes\".

See what wikipedia says..

If you are tossing a coin, the output will be either head or tale. But in multiverse theory we say that we will have both the ouputs and it is splitted in to two \"parallel universes\". In one universe you will be continuing with the head output and in the parallel one you will be continuing with the tale output.

To know the difference between parallel and alternate consider a more detailed example. It is known as \"Quantum Immortality\"

Imagine that a physicist detonates a nuclear bomb located beside her. In almost all parallel universes, the nuclear explosion will vaporize the physicist. However, there should be a small set of alternative universes in which the physicist somehow survives (ie. the set of universes which support a \"miraculous\" survival scenario). The idea behind quantum immortality is that the physicist will remain alive in, and thus able to experience, at least one of the universes in this set, even though these universes form a tiny subset of all possible universes. Over time the physicist would therefore consider herself to be living forever.

Now the next question...

Has the string theory changed at all after its now called the m theory?[/b]
M theory generalised all the different string theories in to a single theory. It was believed before 1995 that there were exactly five consistent superstring theories. It was shown later that these super string theories were related by dualities, which allowed physicists to relate the description of an object in one string theory to the description of a different object in another theory.

So scientists thought that these five theories are nothing but reflections of a single truth in "five different mirrors". So the scientists decided to find out the original theory and they discarded the mirror images. And that single underlying theory is named as M theory.