I tried to find something like that a few years ago and discovered that there's something about my USB keyboard that doesn't like having its LED toggled numerous times a second. Either the LED would get stuck in a particular state, or the keyboard itself would go nuts requiring a reboot.
I gave up and ended up using FloatLED: http://www.stone-oakvalley-studios.com/index_software.php
-Ralf Maximus
I had spent long hours searching for a solution and after I post this message, I find a couple of software solutions.
FloatLED is based on this software DriveGLEAM found at
http://www.dirtcellar.net/What is cool about this program is that you can hook up and control LEDs from the
parallel port.
I also found an autohotkey script at
http://www.autohotkey.com/forum/topic17954.htmlWhat I would really like is just a stand alone program that would do job without all the bells and whistles.