Linux

Someone beat me to it. I've been sick of having hard drive failures on my little Thinkpad that I use to do most of the house's packet routing and shaping. I've been working on getting a 44-pin laptop IDE to CompactFlash adapter that will actually fit correctly in the bay of the Thinkpad 600E.

http://www.cflinux.hu/

My original thought was Fedora Core 4, stripped down, and mounted r/w only sparsely but it looks like this distro is made specifically for Compact Flash.