Hi,
Generally in order to register a plugin you should use Plugin Registration Tool (
http://code.msdn.microsoft.com/crmplugin), unless you want to write your own code that will register plugins. In regard to the plugin you mentioned, you will have to read its documentation / comments in order to check which message you should register it against.
I hope that helps,
Kuba
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Kuba Skałbania, Netwise