Small Distro Question

[Jonathan Younker]

Hello,
My name is Jonathan, and I've been lurking on the list for a little while 
now.  I've been using Linux for about a year, mostly in a library 
environment (money's tight for libraries these days).
We're looking into setting up a bare-bones DNS server as a fail-over for 
the library's main ones housed in the school's IT department.  It would 
only run the DNS software and SSH.
We've got some old 486s that have 500mb HDDs and 16mb RAM.
My question:
Are there any distros that anyone would recommend for something like this?
I've played with Slackware, but I've heard of some smaller 
distributions.  Does anyone have a favourite?
Thanks,
Jonathan.