Starting on 9,10 as GUEST

[Bertrand MARLIN]

I try to explain with my poor english...
 
My situation : I am a french teatcher in a secondary school and i am the
administrator of all the computers of the school
                      Reaparing, installing managing all of the 80 
 machines in the classrooms.
 
 About Ubuntu :  I use Ubuntu from the beginning at home. I am constant
 user of it .  I try to change for better some proceedings and build
 programs for school. I haven't finish because I have lots of ideas...

 
 Last year I install on all of computers in my school :  Ubuntu 9,04 as
 you can see on the picture of a classroom join in this mail.
 At this time i ask students to get an USB Key to save their works and
 use only the guest session. (Only for protection of the system)
 To do that,  I use an addon menu and a script witch permit  to every one
 to start the machine on the guest session at the logon menu of Ubuntu (
 I explain to do it for others teatchers on my web site :
 http://mproduction.nuxit.net.). I keep the admin count to install
 softwares and makes upgrades (only for me)
 
 I don' want that eache student log on Ubuntu with a standard user,
 password on spécific name or count , ONLY as  GUEST
 For a school it is very usefull.
 
 With the new version of Ubuntu 9,10, the GDM change... and my script
 doesn't work...
 
 My question is.... COULD YOU HELP ME or explaine to me  how I can  have
 in the logon menu  a possibility to use ubuntu 9,10 à the logon menu as
 a guest so that i can upgrade  and keep  my methode of protection of the
 system as i have done in Ubuntu 8,04. I havent found a solution today...
 i can't  upgrade  form 9,04 to 9,10.
 
 I would be very glad if an engineer from Ubuntu on a developper show me
 how to transforme my script  or show me a new proceeding  to start as
 GUEST in Ubuntu 9,10...
 
 Please , i believe in you, in Ubuntu, Help me, I wait for your answer.
 Long life to Canonical and Ubuntu.
 
 Best regards,
 MARLIN Bertrand