Python palindrome checker
Writing functions

A palindrome-checking function should accept a string parameter and return a result.  Your function takes its input from the keyboard (or stdin), which makes it not reusable.  If you want to accept keyboard input, it should be done outside the function.

Even more unusual is the fact that you return None if it's a palindrome, and return 0000 if it's not.  Why so many zeroes?  Why are both return values falsy?  The convention would be to return True or False.

Implementation

You're doing a lot of unnecessary things.

You can index and iterate over strings directly.  There is no need to convert it into a list.

There is no need to handle odd and even lengths as separate cases.

Der_Lett (a cryptic abbreviation for "dernière lettre"?) actually isn't the index to the last letter — it's off by one.  (Your code is correct, but weird.)

Style

PEP 8 naming conventions apply to your variable names, même en français.  That is, they should be lowercase.

Counting loops are nearly always better done using of range(), xrange(), enumerate(), or something from itertools.

Suggested solutions

Here is a simple loop that does the job.

def verifier_palindrome(mot):
    centre = len(mot) // 2
    for decompte in range(centre + 1):
        if mot[decompte] != mot[-decompte - 1]:
            return False
    return True


Here is a more compact way to write it, using a generator expression:

def verifier_palindrome(mot):
    return all(mot[i] == mot[-i - 1] for i in range(len(mot) // 2 + 1))