? renaming files using the command line

In principle the command line would be a mighty tool to rename files,
but I just don't seem to know the right commands,
and google searches in that respect don't seem to be very elucidating.

The problem:
I have to rename about 500 files.
The file names have upper case letters, and I would like to change them
to lowercase letters.

So I thought that commands like
would be a good idea, but then I get
(translated).

On the other hand, using
there aren't any complaints, but just as well, NOTHING happens.

Even DOS had the command `ren' that would have made it,
but with bash / Linux ?

For many of you this probably is a trivial task.

Thanks
Mike