OK here is brief description what I did, I will add to it if I can get buttons working:

This describes how to get USB2LCD+ running on NSLU2 Linksys Network Storage with Linux kernel 2.4.22-xfs (it may work on other distributions as well.).
More info on NSLU2 and Linux can be found here http://www.nslu2-linux.org

run ipkg to determine if usbserial is installed
# ipkg search '*usbserial*'
kernel-module-usbserial - 2.4.22.l2.3r63-r21 - /lib/modules/2.4.22-xfs/kernel/drivers/usb/serial/usbserial.o

if it is not, run ipkg to install it
#ipkg install kernel-module-usbserial

plug in the display
run lsusb to determine vendor and product number
# lsusb
Bus 003 Device 001: ID 0000:0000
Bus 002 Device 001: ID 0000:0000
Bus 002 Device 009: ID 5bcd:5bcd
Bus 001 Device 001: ID 0000:0000
Bus 001 Device 002: ID 13fe:3423 Kingston Technology Company Inc.
Bus 001 Device 003: ID 0bc2:3300 Seagate RSS LLC

in this case, Vendor ID is 5bcd and Product ID is 5bcd
(note: USB2LCD+ is always 5bcd / 5bcd unless the firmware source code is changed)

then manually bind the driver
#insmod usbserial vendor=0x5bcd product=0x5bcd
before connecting the USB2LCD+ display

if usbserial module was loaded before, it will need to be removed first using
#rmmod usbserial

then run dmesg to see which port was assigned to your display
#dmesg
...
...
...
hub.c: new USB device 00:01.0-1, assigned address 13

Device descriptor:8 bytes received.
Device descriptor:18 bytes received.
usbserial.c: Generic converter detected
usbserial.c: Generic device with no bulk out, not allowed.
usbserial.c: Generic converter detected
usbserial.c: Generic converter now attached to ttyUSB0 (or usb/tts/0 for devfs)
...
...
...


I used lcd4linux to drive the display, here is the Display section of  lcd4linux.conf file that works with my display
...
...
Display SerialLCD {
    Driver  'MatrixOrbital'
    Model   'LK204-25'
    Port      '/dev/ttyUSB0'
    Speed     '9600'
    Contrast  '160'
    Icons     '0'
}
...
...


That's it!

Roman G.