I have this same problem with Debian Etch and with Ubuntu Feisty, but only in my Desktop, In my Laptop an IBM T30 with Ubuntu Fesity installed works great, well the problem is:
As soon as I start my PC and while it turning on eth0 (my only one interface) it gets the IP from DHCP I could see by doing
tail -f /var/log/messages | grep dhcp
On my CentOS DHCP server, well then when I entered my session I immediately see the network-manager-gnome applet as “not connected” and I have to click on it and select the only one option “wired connection” and once again it ask for an IP to the server, so what I did?
I de-installed network-manager network-manager-gnome
sudo apt-get remove network-manager
then reboot and no everything works just fine!