Thanks alot Sherlock for suach a detailed response, it helped alot.
Now iam working on DIF, the thing as i understand is that in DIF the decimation takes place in Frequency domain it means that the input is unscrambled and we modify it at the out put, but i have tried this thing several time, i can't not obtain the same results as from DIT..
could you please tell me about the DIF algorithm an example will be a great big help for me..
INfact if you could tell me more about Butterfly this

___ 1 ___
* *
-j * *
* *
* +j *
----- - 1 -------

if cculd explain this picture (its not that clear although) it will be a great help..
thanks in anticipation,
Asim Ali