Does this exist?
 

I use XDM as a login manger. The one thing I to have on the login screen that it currently doesn't have is a little window with reboot & shutdown buttons in it. Ideally, a GTK app so it can fit in with the rest of my curren theme.

Is there such an app already in existence, or should I (who gets baffled by VB) prepare myself for a long evening with glade and the GTK.org tutorial to try and work it out for myself?

It seems like something so simple should exist already, but I'm damned if I can find it if it does. . .

Have you tried gdm, instead of xdm? It may also be possible with xdm, just a configuration option.

I prefer XDM. I only have one WM installed (FVWM) so don't want features like selecting which WM to load. . .

After a quick search ( google is your friend ), see this page on xdm shutdown button.