How to append entries to the desktops/window managers list?

[Kyriakos Sidiropoulos <ksidirop csd uoc gr>]

Hi all you guys. You know I am having a problem figuring out how gdm 
'understands'
how to lay out the list of available window managers/desktops when you 
click on the
'session' button (or whatever it's called). I want to append one more 
entry to this list. Is
this fisible? Thanks in advance.

Cheers,
Kyriakos