Ok I've screwed around with my source a lot and don't feel like pulling a fresh copy to double check this, but I'm like 99% sure this will work.
You need to be able to compile armagetron source code. If you don't know what that means, find out and then come back to this post.
This is using armagetronad-0.2.8.3_rc2 from http://beta.armagetronad.net
Open up src/tron/gCycle.cpp in a text editor.
near the top, find the lines
#ifndef DEDICATED
#define DONTDOIT
#include "rRender.h"
#endif
and add
#define DEBUG
right below them. Compile the source and you've now enabled the ability to have a better chatbot. Now we need to activate it.
You can use 5 instachats to activate the bot, but you can also put the commands in a cfg file.
/console CHATBOT_DELAY 0
/console CHATBOT_DECAY 0
/console CHATBOT_MIN_TIMESTEP 0
/console CHATBOT_NEW_WALL_BLINDNESS 0
/console CHATBOT_RANGE \
The last one is the one you want to play with... for a relaxed almost human style bot, set it to 1 or more. For insane moves without suiciding set it to something like 0.05, any lower will usually cause it to spin itself to death. Simply go into chat mode to see it in action.
This will not give your bot learning ability, and it will suck at getting through digs, but it will be better than many players out there.
Enjoy.
P.S. - I haven't tested this on a slow computer... if your computer bogs down when you do this, try setting CHATBOT_MIN_TIMESTEP to 0.01 or something.