I'm attempting to give users a choice of customized UIs when they login. One will be a standard Gnome session. The other would be a custom UI. I'm not sure if its possible to base the custom UI off of Gnome at the same time or if it would be easier to use a separate desktop environment like KDE or XFCE and then customize it.
In any case the first hurdle is getting adding a new session to the login menu. Most desktop environments create one when their installed so going this route will create one automatically. If I try to reuse Gnome for the custom session I'll need to learn how to create a new session entry manually.
Anyone have any ideas?
Since you mentioned Gnome, I'll assume you're using GDM.
You'll need to create a new .desktop file for your custom UI. Put this file in either /etc/X11/sessions or /usr/share/xsessions. The location will vary depending on your distribution.
You can look at the Gnome file that is already there to see the options. There is also documentation online. You might want to look at GDM Configuration and the Desktop Entry Spec.
As Anthony Lewis mentioned, .desktop files are what you want.
I have one on my MythTV machine to automatically launch the MythTV frontend on boot, as it's just a custom session type.