If you have the money to spend the CS3 suite would be great to have. The thing is you can get a lot of free tools to develop HTML and CSS for web design - or even use notepad. I wrote a post on my blog that goes over a few
web design tools. Some are free, some are not.
Right now, I'm using Adobe CS2 software and Dreamweaver 8 - money - but they work great. I only use Dreamweaver for the coding environment. I like the code assist feature it has, can make you lazy though :) I do all my design directly in code. I don't use the design environment where you can drag and drop page elements. If that's what you are looking for then I would go with Dreamweaver. It's great to have a full version of Photoshop, but there are free alternatives like gimp.
If you have the money you might as well get the latest and greatest. I'd say that with CS3 all the software is going to work better together then with the older suites.