Ok, well.... Since Apple hasn't released us developers from the NDA yet... (GRR!) There's only so much I can say...
First off, you need to know/learn Objective-C. Get yourself a copy of "Cocoa Programming for Mac OS X"... It's widely considered to be one of the best for learning Obj C and Cocoa. While going through that, pay attention to the chapter on Memory Management. The iPhone requires you do it all yourself - no Garbage Collector.
Once you've gone all that, you should be able to figure out how to do most normal stuff in the SDK pretty much no problem as it's similar to Mac OS X programming / APIs.
For doing the dev, if you don't already have a mac, I recommend just picking up a mac mini (or even a used one). I actually got mine from a buddy who wasn't using it anymore. Traded him $300 of purchases at Best Buy for the mini. The only requirement is it has to be an Intel based one (and I believe has to be running Leopard...)
Coming from a Java background, I've been working my way through the Cocoa book after trying to just go straight into the iPhone SDK. Trying to go directly to the SDK had me overwhelmed with trying to get my brain around:
Objective C
XCode 3 Dev Environment
All the SDK / APIs
Easier to take them one at a time...
