help getting a simple graphics tutorial working

I've been trying to get this tutorial to work in Xcode 3.1

http://trailsinthesand.com/exploring-iphone-graphics-part-2/

however, I'm getting 3 errors that I have not been able to resolve.

All three errors are the same, CGContextFillEllipseInRect, CGContextSetRGBFillColor and CGContextClearRect are all giving me the same error.

symbol(s) to found

Do I need to make some changes in my SDK settings? This is very frustrating, just trying to draw a square on the screen - never thought that could be so difficult.

Thanks

Zombii