newbie: help with source code examples.

[Aesop]

Howdy all.
    I know I will be flamed for this one but I am after some example
code that features string manipulatons.

I am an absolute beginner as far as this sort of thing goes, been using
python for a good month or two now, and have now begun on my first real
project. I am attempting to set up a script that can take a text file
that features a filename and a description. What I want to do is
automate the process of generating an HTML table containing a link to
that file, and its description in a seperate cell. The html generation
and file management is not a problem, but what is a problem, at the
momment, is dealing with tabs, and spaces within the initial text file.
I have a system set up at the momment that simply assumes that the
filename and description are seperated by a certain character
combination but what I really need is something that can say identify a
filename by its three letter extension and then work backwards to find
the start of the word. (I am under a Win32 system). How can I do this?
what is the best means?

Any help is appreciated.

In zeros and ones,
Ambrose.