I just downloaded the original Python interpreter from Python's site. I just want to learn this language but to start with, I want to write Windows-based standalone applications that are powered by any RDBMS. I want to bundle it like any typical Windows setup.
I searched old posts on SO and found guys suggesting wxPython and py2exe. Apart from that few suggested IronPython since it is powered by .NET.
I want to know whether IronPython is a pure variant of Python or a modified variant. Secondly, what is the actual use of Python? Is it for PHP like thing or like C# (you can either program Windows-based app. or Web.).
what does "Pure Python" mean?  If you're talking about implemented in Python in the same sense that a module may be pure python, then no, and no Python implementation is.  If you mean "Compatible with cPython" then yes, code written to cPython will work in IronPython, with a few caveats.  The one that's likely to matter most is that the libraries are different, for instance code depending on ctypes or Tkinter won't work.  Another difference is that IronPython lags behind cPython by a bit.  the very latest version of this writing is 2.6.1, with an Alpha version supporting a few of the 2.7 language features available too.
What do you really need?  If you want to learn to program with python, and also want to produce code for windows, you can use IronPython for that, but you can also use cPython and py2exe;  both will work equally well for this with only differences in the libraries.
Is IronPython a 100% pure Python variant?