As shipped, the iLiad does not include linux USB modules. A layer of Phillips originated modules appears:
./kernel/drivers/usb:
-rw-r--r-- 1 arivero arivero 6782 2006-06-23 18:27 hal.o
-rw-r--r-- 1 arivero arivero 9961 2006-06-23 18:27 mscd.o
-rw-r--r-- 1 arivero arivero 17338 2006-06-23 18:27 pdc.o
-rw-r--r-- 1 arivero arivero 42497 2006-06-23 18:27 phci.o
A google search reveals this document:
http://my.semiconductors.philips.com.../UM10012_2.pdf
http://www.semiconductors.philips.co.../UM10012_2.pdf
From it one infers that phci is the Host controller, letting iLiad to act as Host, and pdc is the Device controller, letting iLiad to act as Device. Mscd is a mass storage class device, I guess for the iLiad to act as mass storage device, while a module storage/usb-storage.o is provided for the iLiad to be able to read inserted usb sticks. Hal stands for "hardware access layer" (and yes, it is one step before IBM, in the same way that W-NT is a step after vax VMS), being common to the device and host modules.
Basically, page 21 tell us that if we provide the USB class drivers, they will work as any Host machine should. So the question, er, reduces to find the usb class modules for the usb keyboard in a 2.4.19 arm kernel.