Take a look at workflow.ini

[OperationSettings]
AvailableOperationList[]

ist an array holding all Triggers that will show up in the admin interface to set your workflows on.
You can add right a couple of Triggers of the eZ Modules or your own Modules.

i.e. content_delete or user_activation (added in 4.1)
can simply be added to the list.

I guess you can create own Module - Triggers based on
kernel/content/operation_definition.php mentioned by Bertrand Dunogier

but with the user module triggers already being ready I didn't need to work that out.

Good Luck if thats what will be Your Way ;)
Mark