[plug] How do you switch between KDE and Gnome

[Richard]

I have just finished downloading Ximian Evolution and it installed ok, but 
has changed my default desktop from KDE to Gnome on all accounts in my system 
(a little embarassing :) I was just wondering if someone could give me a 
rough idea of where the settings that dictate the default desktop are kept, 
and are there any pitfalls to look out for in swapping form one desktop/wm to 
another? I have looked through /etc/bashrc and profile, but couldn't see what 
I was looking for. Thanks.
Richard