Fresh Ubuntu 10.10 installation on an Intel Core 2 Duo Box with an Asus motherboard. i86

When I connected the ethernet cable to INSTALL 10.10 using a USB stick, it worked just fine.

When I booted for the first time, however, no internet connectivity via the Ethernet cable.

To be sure, I connected another desktop and another laptop to the same cable, and there's nothing wrong with the router or modem.

I connected via USB (via my cell phone), and WHAM, Internet! Yay!

So, why does internet on this box work via USB, but not via Ethernet? This is a desktop office computer that isn't going to be used for anything graphical/video/etc., so I'm keeping the setup really really basic.

In the meantime, I'm going to go ahead and use an Ethernet-to-USB converter thingie to connect until I find an answer.