Almost any network interface card (NIC) supported by the Linux kernel should also be supported by the installation system; modular drivers should normally be loaded automatically.
On ARM, most built-in Ethernet devices are supported and modules for additional PCI and USB devices are provided. The major exception is the IXP4xx platform (featuring devices such as the Linksys NSLU2) which needs a proprietary microcode for the operation of its built-in Ethernet device. Unofficial images for Linksys NSLU2 with this proprietary microcode can be obtained from the Slug-Firmware site.
The installation system currently does not support retrieving firmware. This means that any network cards that use a driver that requires firmware to be loaded, is not supported by default.
If there is no other NIC you can use during the installation, it is still possible to install Debian GNU/Linux using a full CD-ROM or DVD image. Select the option to not configure a network and install using only the packages available from the CD/DVD. You can then install the driver and firmware you need after the installation is completed (after the reboot) and configure your network manually. Note that the firmware may be packaged separately from the driver and may not be available in the “main” section of the Debian GNU/Linux archive.
If the driver itself is supported, you may also be
able to use the NIC during installation by copying the firmware from some
/usr/lib/hotplug/firmware. Don't forget to
also copy the firmware to that location for the installed system before
the reboot at the end of the installation.