There are 4 steps to set up tomcat 4.1 inside eclipse IDE 3.1, which are defined below;
Step 1: Download Tomcat plug-in.
Step 2: Close eclipse and place it inside plug-in folder of eclipse.
Step 3: open command prompt, go to eclipse home directory and type command eclipse -clean
e.g. E:\Eclipse3.2.1>eclipse -clean
Step 4: on eclipse, go to Preferences and then select Tomcat, select tomcat version you have installed and set the Tomcat home path.
Now the eclipse IDE is ready with Tomcat and we can start developing web applications/tomcat projects. We can start, stop and monitor Tomcat from eclipse.