I've always used Debian testing, currently Wheezy. I did a reinstallation on my desktop that was shelved for eight or so months and used the 200+ MB net install CD image off USB. It did the same, it could not configure eth0. So I did the base installation from what it could do off that CD image, rebooted after it finished into command line (as there was no desktop environment) and continued on from there. I always choose this route anyway as Debian's default desktop is Gnome but I prefer KDE.
Anyway, possibly due to not having necessary networking packages in the net install ISO, it did not load the driver for the NIC automatically. A quick command: lspci showed this for the NIC: Ethernet controller: Broadcom Corporation NetXtreme BCM5751. A quick Google search on another computer suggested it uses tg3 driver. Another command: modprobe tg3 loaded the proper driver, then the command: dhclient eth0 got it connected. After slapping in my favorite sources.list, I updated and continued the installation from command line as I usually do.
Although I don't remember where in the Debian installer process, there is the option to go to command line when things are not going well, it is here you can figure out what NIC you have, and at some point down the line if not at this point, you can apply the driver and bring it up with the dhclient command and continue the installation.