Replacing the Compact Flash card adaptor by a CDROM drive, I find that Tinycore Linux (v2.7) loads and runs perfectly.
A CF card with DSL 4.4.10 runs happily when substituted for the standard firmware.
I find that someone in Germany has pressed one of these into service as an IP-COP based firewall.
[December 2018] Original link: http://www.ipcop-forum.de/galerie/proenz.php now seems to require a username/password login.