It's not really a lockup (having the same problem) What happens is the mouse doesn't power up when its on the PS/2 adapter. Unfortunately, leaving both the keyboard on USB and mouse on USB results in the loss of powerup for the keyboard. Unplugging and replugging the keyboard generally fixes this.
It seems that this has been resolved in revision 1.1 boards. I've got a 1.0
I tried the OrangeWare USB 2.0 driver from ASUS and Leadtek, but it does nothing to fix this problem.
Peace