this may help rooz, who knows...

I just tried for the first time a setup like you describe (cheap imation keyboard), and did pretty much what you did... initially it only recognised keys that mapped to the n900 keyboard and maybe tab & escape (although I once accidentally triggered a special character I couldn't work out how to get at them either - anyone: what's the equivalent of the blue arrow button?)

I already had extkbd installed in preparation... I opened it (External Keyboard in the n900's Settings), chose a slightly different likely generic keyboard layout (ended up typing in arabic... when back and found "USA" option...) and after that it worked like a normal keyboard.

[I am very pleased about this, by the way. Thanks!]

Only tried it the once... not sure if you have to wake up extkbd every time.

Also, it did seem to chew through the battery a bit, so I will get a powered hub if I want to play with it for any length of time.

Thanks again. I just love that you guys made this phone better than the manufacturer said it could be.