Download the Squeak Virtual Machine for Linux from http://squeak.org. After you untar it, rename i686-pc-linux-gnu to i686-pc-linux-gnulibc1 before installing the Squeak VM.
Alternatively, you can use apt-get to install Squeak:
To use Apache to serve files for the Seaside app, Seaside's own internal web server is bypassed. So the files that Seaside normally serves from its internal libraries need to be extracted into Apache's file serving location. Here's what I discovered:
To start your Seaside application for a given port number, say, 9090:
squeak MyApp.image "" port 9090 &