[VulnDiscuss] Main thread's exception handler

I have a question. Does someone know something about this WinZip32 MIME Parsing Overflow Proof of Concept Exploit
The author say:
/*
In this exploit, I've chosen to install our code as the main thread's top exception handler so that when exception is triggered at 0049C012,our code will be called to 'handle' it... =p
*/

Does someone know where in memory is this "main thread's top exception handler"?