hmmm I believe I have seen this behavior before and can't remember if a fix was given. You should have something like net-misc/networkmanager-0.9.2.0 installed. I remember what a pita it was with a manual config, but I since have switched to DHCP and config settings in the router for the MAC address. Seems NM rewrites the config files on each reboot. I think one solution was to lock the file down so nothing could make changes to it.
I'm wondering if WICD wouldn't work better since it seems it's still a pita with manual stuff. Our wiki should have a howto for wicd.
Themeing e17, sure, but you'll need to look up the e17 documentation or look at something like http://e17-stuff.org/