First, create a script that starts only what you want, and put it in an appropriate location like /usr/local/bin. For instance, this script starts the Metacity window manager (you'll experience some difficulties if you don't run at least a window manager) and Eclipse. (There are some fancier things you can do, for instance in this example I showed how to restart the program if it is exited.)
/usr/local/bin/eclipse-kiosk.sh:
#!/bin/sh
metacity &
eclipse
Then, make it executable by running chmod +x /usr/local/bin/eclipse-kiosk.sh. Now, create a desktop file for it in /usr/share/xsessions.
/usr/share/xsessions/eclipse-kiosk.desktop:
[Desktop Entry]
Type=XSession
Exec=/usr/local/bin/eclipse-kiosk.sh
TryExec=/usr/local/bin/eclipse-kiosk.sh
Name=Eclipse Kiosk
Now, Eclipse Kiosk will appear in the GDM sessions menu and GDM can be configured to log in using it however you want.
