EDIT:
evkb-0.2 Application You can use your USB keyboard with your iLiad with this application!
I've downloaded the linux-2.4.19-rmk7-pxz2-irex1 kernel sources and patches from the iRex website. The kernel sources appear to have the patch already installed, so it is not necessary to reapply it. There is no .config file included in the tar file (and 2.4 doesn't support /proc/config.gz), so I made some guesses and built input, hid, evdev and keybdev as modules (abbreviated .config):
CONFIG_ARM=y
CONFIG_ARCH_PXA=y
CONFIG_MACH_PXA_IREX_ER0100=y
CONFIG_INPUT=m
CONFIG_INPUT_KEYBDEV=m
CONFIG_INPUT_MOUSEDEV=m
CONFIG_INPUT_MOUSEDEV_SCREEN_X=768
CONFIG_INPUT_MOUSEDEV_SCREEN_Y=1024
CONFIG_INPUT_JOYDEV=m
CONFIG_INPUT_EVDEV=m
CONFIG_USB=y
CONFIG_USB_DEVICEFS=y
CONFIG_USB_HID=m
CONFIG_USB_HIDINPUT=y
CONFIG_USB_HIDDEV=y
CONFIG_USB_KBD=m
CONFIG_USB_MOUSE=m
CONFIG_USB_WACOM=m
I'm able to load them and it detects the USB keyboard/mouse on the port and I can disconnect/reconnect them without problems, but once I hit a single key it hangs the device hard. If I do not load keybdev, I can try to read /dev/input/mouse0 or /dev/input/event[01], but I never see any events in any of them. If I load the old BP usb keyboard/mouse modules (usbkbd.o) I do not see any results, either, but at least it doesn't hang.
dmesg output, although I don't have any after the hang:
usb.c: registered new driver hiddev
usb.c: registered new driver hid
input0: USB HID v1.00 Keyboard [0d3d:0001] on usb1:2.0
input1: USB HID v1.00 Mouse [0d3d:0001] on usb1:2.1
hid-core.c: v1.8.1 Andreas Gal, Vojtech Pavlik <vojtech@suse.cz>
hid-core.c: USB HID support drivers