The location to edit network.conf is from Netbox/Configuration tab/Network :
Click the edit button on the right,leafpad opens /etc/network.conf , make your changes,save,and close.
There is a ->Change button you click to save if it's a fill in the blank to edit a config file  scenario,for example see Control Box/ Bootloader, Initialization, Login Manager tabs.

"Where could I report this bug to get it fixed"

Here : http://labs.slitaz.org/issues

@mojo: I can edit /etc/network.conf with an editor. That's not the problem. (nor do I need netbox for that ;-) )
But I would think that if the setting, under the 'Static IP' tab of netbox, are modified, then netbox would save those settings back into the /etc/network.conf file.
According to the netbox script, this ia also the intension, but fails do to qouting errors in the part of the script which is later interpreted by gtkdialog.

@Erjo: Thx, I'll give it a shot.

Now fixed: http://hg.slitaz.org/slitaz-tools/rev/c2eeac9343bf

Thx!!!

BTW: "now fixed" does that mean a stable image, downloaded today, will already have this fix or is this something fixed in cooking?

Slitaz seems to leave the downloadable stable iso broken. 

Slitaz leaves the downloadable cooking iso broken at least sometimes. 

I asked a question similar to yours a few years ago about frequency of updates to cooking images but have not received an answer yet.

@Slitaz: Yep, that is also my perception, that isos are left broken.

The result is that SliTaz newbees that have the courage will ask the same forum questions time and time again at nauseam...

Less adventurous newbees will just move on to another distribution...perhaps never to come back.

In my case, it took exactly a week to get this old PII running like I wished.  I learned a great deal thanks to you people in this forum, but on the other hand some of that time might have been saved, had the iso/packages not have been left broken...