rename files

can any one help me out with this. I know somebody must have done it
already.

i have a directory with 901 files in it.
i need a script the renames the files. basically i need it to take
anything that is not a number,letter, or "." and change it to an "_".

ie. "Charlie's Root.zip" - will become "Charlie_s_Root.zip"


perl/sh/bash, whatever, dosn't matter. :)

Thanks