GDM default locale--can't set

["Mumia W.." <paduille.4061.mumia.w+nospam@earthlink.net>]

I can't seem to set the default locale to en_US.UTF8 for GDM. When I 
change the settings at the GDM window, it offers to make my new locale 
the default. I always say "Yes" to this prompt, but whenever I log in to 
GDM again, I get the old default: iso-8859-1.

The Gnome help pages say that I can define ~/.dmrc, I can set the 
language for my account, but this does not work; the file is completely 
ignored. Also, ".gdmrc" is ignored. How can I set the default locale?

I'm using i386 Sarge with Kernel 2.4.27. GDM is 2.6.0.8.

Thanks in advance.