I'd start by getting a good book on C until you get a good handle on the C language. If you know Pascal already, C won't be hard to learn at all. I used Dave Mark's
Learn C on the Macintosh back in the day. It was a pretty good book, but by now it's a bit dated since it assumes you're using an ancient version of CodeWarrior in System 7. I'm sure there are some good books on C out there, though, and even regardless of this, the differences in the IDE shouldn't be that much of a problem, anyway - the C language is still the same (although there might be some minor things not covered by an older book such as the Mark book, such as how to take command-line arguments, which wouldn't have existed in OS <=9).
Anyway, once you have a good understanding of C, I'd read Apple's PDF file on Objective-C as it is pretty concise and a quick read but nevertheless does a pretty good job explaining object orientation and the like. Once you've gotten this far, there are a lot of good books on Cocoa (Aaron Hillegass's book seems to get recommended a lot) and lots of info on the Web as well, such as
http://www.stepwise.com/ and
http://www.cocoadevcentral.com/.
Hope that helps,
Charles