mouse cursor (question)

["Daniel Godas Lopez" <siro eurielec etsit upm es>]

id like to now which part of gnome or the xserver is the one that
changes the mouse cursor to a clock when i click on an icon to launch an
application. 

i have another question, how does that program notice that the
application has been loaded so it can change the cursor back to its
normal state?

thx for ur help guys :)