How do I create batch file to rename large number of files in a folder?

I'd like to rename a large number of files within a folder on a WinXP system, preferably using a batch file.

The files are currently named like this:

Vacation2010 001.jpg
Vacation2010 002.jpg
Vacation2010 003.jpg

And I'd like to change them to:

December 001.jpg
December 002.jpg
December 003.jpg

How can I perform this operation??