I own an nslu2 on wich i run debian, for use as a small home-server and place from where i can ssh to the rest of the network
for those of you that are looking how to do this, please see this page
annyway getting it to produce a sound, anny sound can be quite usefull when running scripts and cronjobs.
First install beep
$ apt-get install beep
on a normal Debian system you would just give it the beep command
but to get your nslu2 to sing you should go
$ beep -e /dev/input/by-path/platform-ixp4xx-beeper*