>>I found some useful Forth code for this on some Linux site and I already
>>adjusted this Forth code, but... I am having trouble putting the code
into
>>the OF variable "boot-command" (which is exuted upon booting).
>Can you point me to the site - or maybe send me the code you modified?
>I'd like to play with it

Have a look at http://www.linuxppc.org/userguide/bootMenu.html.
Make sure that you read the section at the end of the document; some typos
in the code presented earlier are corrected there.
The code itself is fairly straightforward once you know a bit of Forth. You
can find a simple introduction to Forth on Apple's developer site (do a
search for Forth and/or Open Firmware).

>Sorry can't think of anything here other than, try it with another
keyboard?
(Another keyboard is a bit of a problem, because it's a USB keyboard and I
don't have a second one, nor do I know anyone else who has one...)

About my weird problem: I was playing with the idea of using the
boot-command to build up a menu command in pieces. But my knowledge of
Forth is so limited that I don't even know how to copy the contents of one
variable to another one.
This morning, while driving to work, I came up with the idea of putting the
various boot-device strings in device aliases ("devalias" in OF) using the
limited boot-command configuration option in Mac OS's System Disk. (I guess
this sounds a vague...)

     jan