Since the response has been so high on this, i decided to make a quick test release before i go away for the weekend.
you need Nexuiz-svn or 2.5.2. may or may not work with older ones.
then get this file and put in nexuiz/data:
http://zdev.dvrdns.org/tmp/spiderbot.pk3
edit: you need http://zdev.dvrdns.org/tmp/spider-config.pk3 too.
extract the progs.* and cdprogs.* form it and place in the nexuiz/data folder.
launch nexuiz, type "exec vehicle_spiderbot.cfg" in the console then do a "map test16" or a "map opentest"
just run into a unoccupied spider to start driving it. bind a key to +use to exit it.
have fun =)