Hi YellerPuma,
Goto System -> Preferences -> Sessions. Click on Pidgin. Either uncheck Pidgin (perhaps you may want it to startup (by default) at some time in the future, or click on Remove in order to remove it from being included in the startup application sessions.
On next login, Pidgin should not startup automatically. Do the reverse to cause Pidgin to autostart in the future - i.e. either check it (if you now uncheck it), or Add it making sure it is enabled.
Here is a link to the
Gutsy Gibbon Starter Guide.
-- Tom