Making Your Decision
So which program should you buy? The answer is, it depends. If you are on a smaller budget and will use your graphic editor only for exporting to the Web, I recommend Fireworks. It is a lot more affordable and has all the functions that the average Web designer will ever need when working on Web projects.
On the other hand, if you are willing to spend a bit more and you work on both online and offline pieces with your graphic editor, I recommend buying Photoshop 6. It has more features made for "real" digital artists, and does not focus much on Web graphics (although in this latest version we can see that Adobe has made successful attempts to customize parts of the program for Web designers). I recommend that you take a look at both products' Web sites and then decide which one works best for you!