Are you going directly to
Tomcat on the Linux box or via it's web server?
If it's via the web server (probably Apache), you may need to define the /forums URL as a TC webapp in the config file. (Note: some installs are set up to do this automatically every time TC and HTTPD are restarted).
You should also check to see if the forum web app is actually registered and starting. You should be able to do this with Tomcat's tools (newer TC versions use /manager/html can't remember if this is valid for 4.1). TC generally gives a different message than 404, but 4.1 might not.
An alternative to the webapp manager is to check the TC logs to verify that jForum is truely starting. You should see some info from net.jforum classes there.
Finally, 4.1 is ancient.
[originally posted on jforum.net by monroe]