Is it possible to add the nav system into a 05' 530 with I drive?

It is, but it's going to cost a lot more than it would from the factory.

That, and BMW doesn't ship CCCs without a PUMA case.

If you want to get a nav system, get a separate one from Best Buy or something. It's too difficult (not to mention expensive) to install one on a vehicle that doesn't have one already.