setting $HOSTNAME during install

[Bert De Vuyst]

Hello,

When you boot a FAI floppy, it sets HOSTNAME=ip-number.
The configuration script of postfix returns a error on a hostnames only 
containing numbers.
I did set up a class configuration script witch asks for the hostname 
(if_hostname) of the new machine, and ends with 
export HOSTNAME=$if_hostname
But this doesn't seem to work.
I did check out /tmp/fai/rcS.log. $if_hostname is set, but the line 
export HOSTNAME=$if_hostname doesn't seem to work.
How do I have to set the hostname during install?
Or is it not possible to change the hostname during install.

Sorry if this is a dumb question,

Bert.