>>Can't you use sound instead of messing with the keyboard lights?
>
>What is a computer doesn't have a sound card? My at work doesn't...

Yes that's true, but most reputable Pc's can produce at least some kind of beep

I just seems to me that flashing numlock lights etc is a non standard way of reporting incorrect keyboard input, Also i'm not sure the user would see them any better than say a Flashing red bar at the bottom of the screen (even though I don't like this idea either!)

Other ways to alert the user :-)
Open & close the CD Tray
Grind the A: Drive
Change monitor resolution so you get that Gnuung noise
Find a way to press the DeGauss button (Oh yeah)

that's all I can think of...

Oh yeah..last one.. buy a sound card! :}