If I update Thunderbird from 2 to 3 once I've clean installed 2009.2 and my profile, will that be a smooth operation ?
I no longer use TBird but if it was me I would install the 2009.2 system and then open TBird and import/move/whatever your emails into it and only when I was happy that everything was hunky dory would I update TBird to version 3 (you may want to go to the TBIrd web site - or search on Google - to see what they suggest for the best way of importing settings and emails etc)
Also, I did mention adding the Gnome stuff to enable KDE or Gnome sessions - is this do-able ?
Yup - that can be done. Again I would suggest getting your KDE system setup in a way that your happy with everything and fully updated and then go about adding the Gnome desktop stuff.
To add Gnome open Synaptic and select the "Custom" button, and you will see lots of task-xxxxxxx items ( these are "tasks" for setting up different desktops or printers or virtualbox etc)
The ones you are interested in is:
task-gnome-minimal (which sets up the Gnome desktop with the minimum amount of packages etc)
task-gnome (which sets up the FULL Gnome desktop)
So it will be your decision for which to install. I know some users do the minimal install first and THEN add the full task-gnome on top of that but its not essential doing it that way.
When you are happy with your setup there are also the lxde
and the enlightenment
desktops in that same Synaptic area for you to consider at sometime BUT AGAIN
I would suggest getting your KDE setup configured properly first and getting your data safe (and setting up back-up routines
) before jumping in too deep.
Good luck and have fun