Problem in date format

Hi EVERY one

I have very Big Problem i am making one report where two type of date format is appearing like

MM-DD-YY 03-08-2010

and

DD--MM-YY 08-03-2010

when i try to change first format it picks 03-Aug-2010 and in second format it picks 08-Mar-10

I need all dates in DD-MM-Year format

so can anyone tell me how can i do the same there are 6000 cells and i got headache because of this

Kindly help me