Button to autonumber files

Hi, I would like a button that can take a bunch of files and add numbers with leading zeros to the front of them. Could someone show me how to construct this? Thanks

Thinking about this more, what I actually want is a button that autonumbers like so:

Understanding buttons.MP4 TO 01. Understanding buttons.MP4
Navigation buttons.MP4 TO 02. Navigation buttons.MP4
Setting rollover states.MP4 TO 03. Setting rollover states.MP4

This seemed to get the job done. If anybody has a better suggestion please show me. Thanks

@NoDeselect Rename NUMBER=01 REGEXP PATTERN="(.*)" TO="[#]. \1"