This program lets you use any wacom compatible tablet as a midi controller, which can be used with most VJing software, as well audio and other software.
For midi tab to be useful for software you must use a program like midiyoke or maple midi (will write review later) so you can route the midi out of midi tab to another piece of software. i have writen a guide on how to do posted here on vjcentral.

The Graphire3 4x5" is Wacom's smallest and cheapest Tablet at only $99US. Despite it's size it's not a toy and if you've never tried one you don't know what you're missing out on.
If you do any kind of Photoshop, Paint, Video Editing or Compositing work you should really consider buying one and it makes a surprisingly good scratch controller for VJ programs as well.