I'm starting to study Python, and for now I like it very much. But, if you could just answer a few questions for me, which have been troubling me, and I can't find any definite answers to them:

What is the relationship between Python's C implementation (main version from python.org) and IronPython, in terms of language compatibility ? Is it the same language, and do I by learning one, will be able to smoothly cross to another, or is it Java to JavaScript ?
What is the current status to IronPython's libraries ? How much does it lags behind CPython libraries ? I'm mostly interested in numpy/scipy and f2py. Are they available to IronPython ?
What would be the best way to access VB from Python and the other way back (connecting some python libraries to Excel's VBA, to be exact) ?
1) The language implemented by CPython and IronPython are the same, or at most a version or two apart.  This is nothing like the situation with Java and Javascript, which are two completely different languages given similar names by some bone-headed marketing decision.
2) 3rd-party libraries implemented in C (such as numpy) will have to be evaluated carefully.  IronPython has a facility to execute C extensions (I forget the name), but there are many pitfalls, so you need to check with each library's maintainer
3) I have no idea.
Python - IronPython dilemma