In very short, to resolve this problem you need: >From installation guide: http://www.debian.org/releases/stable/i386/ch06s04.html.en you can get to: http://cdimage.debian.org/cdimage/unofficial/non-free/firmware/squeeze/current/ or http://packages.debian.org/search?keywords=firmware and there in packet firmware-linux you can find the needed bin-file (that d101m_ucode.bin you saw in installer's log). Now, all you need - extract it from tar or deb, write to floppy or flashcard, start installer (preferably in expert mode), and before the network confuguration step switch to another console (alt+F3), plug floppy/flashcard in, mount it with mount -t vfat /dev/..... /some/directory and copy bin-file to /lib/firmware/e100/ (you need mkdir before that). And after that you are able to switch back (alt+F1) and continue installation.
Of course, bug is still in place - problem with firmware is not caught properly by installer, installer continues trying to setup DHCP network using unusable NIC, wrong error report is displayed to user, get-firmware-from-floppy menu item becomes available long after it is actually required to be used for successful PXE-network-installation, and that item is misnamed as really it's name should be "from-removeable-media", as USB-flashcard is actually supported too (and, may be, card-reader cards too).
