I'm getting by a different way than most, in case you're interested.
First I looked up online tutorials on C. Unfortunately I lost the bookmark but I did have one particular website that was all I needed to learn everything, and even to understand pointers though I still don't see how they're useful...
After I got my C background, (you just need to know the basics of C, you don't have to be able to write a program or anything.) I got hillegas' book.
I've been working through the book, but in my own way. I work through it for a bit, but I get bored easily
so when I can't take it anymore I look through the table of contents and pick an interesting subject. I then read that chapter, to see if I can handle learning it. Then I go to x-code, and with a mixture of the book, google results, and the xcode documentation I learn how to do whatever it is. This forum and the cocoa-dev mailing list are useful too.