m0n0wall is not restricted to specialised embedded PC platforms. The generic PC images will run on most general PC hardware and other embedded PC platforms, such as the Lex Light range of PCs, as long a they meet a few basic minimum requirements:

Intel Compatible i486-100 or faster processor 64MB RAM 2 network interfaces supported by FreeBSD 4.9 > 8MB IDE Hard Disk or IDE Compact Flash Card
or ATAPI Floppy Disk Drive, IDE CD-ROM Drive and BIOS that supports booting from CD-ROM (El Torito standard) VGA adaptor

The minimum requirements cover lots of different types of hardware. For those people hoping to re-use old hardware, the 64MB RAM requirement is likely to be most problematic. This is an unfortunate side effect of the system running entirely in RAM and is to allow new versions of the software to be uploaded, decompressed and written to the boot media while the firewall is still in use.

If you have less than 64MB of RAM available, the best work-around on general PC hardware is to use the CD-ROM & floppy disk installation method. As the image upload method of upgrading the software simply doesn't apply (CD-ROM installations are upgraded by writing the new image to CD-ROM and rebooting the firewall), 32MB should be a workable minimum amount of RAM.

Network interface is the other area where you might run into problems, but FreeBSD 4.9 supports the chipsets of most 'common' Ethernet network cards. Check the FreeBSD 4.9 hardware compatibility notes for more information.