I followed the instructions for Debian bridging (http://wiki.aranym.org/manual#proper_debian_bridging_setup) and now I can ping the host machine from within Aranym and vice-versa. The only problem is Aranym can't ping the other machines on the network.
I'm not sure if the problem might be a lack of the "aranym.xif" file. I keep seeing it mentioned in the docs, but I can't find it anywhere in afros or Aranym.
Seeing as I can ping the host machine I'm not sure if it's a problem with my FreeMiNT setup or with my Linux one. Just a case of narrowing things down, but if anyone has any ideas I'd love to hear them :)