If you're intent on creating vector (as opposed to bitmap) based artwork, then Adobe's 'Illustrator' is the design package for you.
Used by the majority of creative professionals, the program is useful for designing logos which can be rescaled without degradation (e.g, they won't pixellate as bitmaps will).
The first version of Illustrator was released in 1987, with the 'CS3' version representing the franchise's thirteenth outing. I suppose you could say that Adobe have had plenty of time to refine the product.
I find Illustrator both useful and incredibly frustrating at the same time.
For a piece of software which resembles 'Photoshop' so closely in it's appearance and layout, it operates in a completely different way.
As a fairly new user, I struggled to get to grips with some of the tools (e.g the bezier tools), which create straight or curved vector line segments. I'm now slightly more adept in using the program, but i've been forced to learn due to the nature of my job.
If you've used the CS2 version of this product, you'll notice some new features. These will be firstly apparent with the new user interface which is cleaner and less cluttered. There's also some 'Live paint' and 'Live colour' enhancements, which advanced users will find easier to use.
Illustrator CS3 is an incredibly versatile product, although I wish some of the tools would react in the same way as they do on it's sister program Photoshop.
Costing over £550, the program is available from Amazon and the Adobe website.
To run the program on a Mac, you'll need at least 2.4gb of disk space and 512mb of RAM.