One way to install Debian on a machine that requires the bnx2 network driver, is to download the firmware, place it on a USB stick and continue as instructed by the Debian Installer. Another quick trick is to use a USB ethernet card and proceed with installing Debian. Then apt-get install firmware-bnx2 and reconfigure the network interfaces appropriately.
bnx2 and Debian
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Managing organized complexity 
There’s also another possibility, appending a gzip’d cpio archive containing /lib/firmware to the original installer’s initrd.gz, as described here: http://wiki.debian.org/DebianInstaller/NetbootFirmware.
Actually, this whole concatenated-gzipped-cpio concept is pretty useful, as it allows overlaying a lot of stuff (firmware, preseeding configuration, custom scripts) to the initrd without unpacking and modifying the original one.
Pretty neat hack indeed!