Is it necessary to set large objects to null when implementing a Dispose() method?
Events and Dispose are not really related. If by "disposed" you mean "collected", then you're right but otherwise your wording isn't very clear.
To add (a late) caveat to this answer regarding references; there are a only a very few scenarios that can lead to a leak and the mostly commonly 'recognised' leak actually isn't. This MSDN blog has a very good writeup:blogs.msdn.com/b/davidklinems/archive/2005/11/16/493580.aspx