Originally Posted by: Whunea half-step is a minor 2nd
a whole-step is Major 2nd[/quote]
While this is true, it is potentially a confusing way of identifying intervals. It is limiting in how you can grasp further knowledge about intervals, scales & chords.

The terms half-step & whole-step are more widely applicable because they are more generic. Whereas, the terms minor 2nd & major 2nd suggest a specific scale degree, instead of "any given" interval inside a scale formula.

Originally Posted by: Whune
the Diatonic Major Scale is
Major 2nd
Major 2nd
minor 2nd
Major 2nd
Major 2nd
Major 2nd
minor 2nd
[/quote]
Again, this is true. But is might be more confusing than clarifying. It's better to think of a scale formula in the more generic terms of half-step & whole-step. That way you get the standard major scale formula:

WS-WS-HS-WS-WS-WS-HS

This helps to better clarify the distances between the scale degrees, so you can get from the formula to this:

1st (root) WS 2nd WS major 3rd HS 4th WS 5th WS major 6th WS major 7th HS 8th (octave of root)

So, in this list you can see pretty quickly that the interval of a major 3rd is 2 whole steps; or a major 6th is 4 & 1/2 whole steps, etc.

On the other hand, using major & minor 2nds as your standard unit of measurement means that the distance of a major 3rd is:

major 2nd and major 2nd.

Or that a major 6th is:

major 2nd and major 2nd and minor 2nd and major 2nd and major 2nd.

This is all true. But using half-steps & whole-steps is a little more clarifying. Make sense? :)
[QUOTE=Whune]
... technically there can be as many different types of scales as there can be different series of intervals between any octave series of notes

Yes, absolutely! You've grasped a very important idea here: a scale is defined by its interval formula. The only thing I would say to improve your understanding is to use the terms whole-step & half-step, instead of the potentially confusing major & minor 2nd.
[QUOTE=Whune]
by the way: why is it called a "perfect" Fifth?

Most other intervals have variations: major or minor 3rd, etc. The 2nd, 4th & 5th do not. Also, historically, aside from the octave, the 5th is the most consonant sounding interval & closest to a perfect ratio (3:2). Finally, the inversion of the fifth is the perfect fourth (distance from root up to note versus distance of octave down to note).

See here for more details:
http://en.wikipedia.org/wiki/Perfect_fifth

Hope this helps!