I would assume you'll need the SDK from Adobe.
where can i get that?
EDIT: I have adobe premiere 7
Will SDK for CS3 work?
I've never seen an SDK for Premiere, but you might want to start your search HERE.
Just a guess, but if Adobe does have an SDK for Premiere, I would think that it would be for CS4.
PS, what sort of plug-in are you looking to develop?
I've never programmed for Adobe, so I can't way with any authority. But my guess is you'll need the correct SDK, and it's unlikely you'll find one for a version that old.
What is it exactly you're trying to do? Maybe we can offer alternative suggestions.