Lets say you have downloaded some game or application that was 50 parts big, and you had to rename them all from .bmp to .rar to extract them.

You can easily create a batch file that does that for you.

Open Notepad

Fill in de notepad:

CODE
ren *.bmp *.rar

Of course, you have to edit dese two extensions to fit de files you want to convert. Save this file as renamer.bat and run it in de directory where you want to rename your downloads.