To answer your question, you would want to run Arena in either Windows 98 or DOS on that computer. Don't even bother with DOSBox since, if the computer is that old, it'll be deathly slow if it even runs at all.
I never had any problems running under Windows 98, but if you use DOS be prepared to deal with potential memory management issues.
If you have any more problems, you may want to start a new thread. Troubleshooting was not what this one was intended for.