1. Validation doens't catch every aspect of how you can write bad mark up. You can have both validation and bad mark up in the same package.
2. Since when did you get the idea that web dev was so simple? In fact, those top 5 browsers are the one messing up and force you to resort to CSS wizardry. And I'm not pointing the finger to IE alone. Each has its issues, and every new version resolve some and bring some with it.
3. There is a 1-in-1 chance your CSS code will not be valid I know I live by that rule. There are errors, which you should fix, but there is "invalid" code you just need to get the job done.
Thanks for everyone's feedback. I'm a one-man-band working on one computer so having the option of personally downloading all the browsers and various versions doesn't seem plausible to me. Besides, I really like the idea of easily flipping through different browsers and overlaying (onion skin?) different renderings.
Browserlabs looks good since I work in Dreamweaver. I can't find where they list the price packages. How much is it?
Another service I found that looks like it would be really good is Multi Browser Viewer. www.multibrowserviewer.com The cost is $140 a year.
One concern I have is once I see that a certain browser/version is rendering my page badly is I have no idea how to fix it!! For example, I looked at a page using browsershots.org and the page looked good in all the browsers I selected except for MSIE 7. For some reason it was dropping the 1st column down about 800px. So now I know that there's a problem, but am unsure what to change in the code to fix it AND keep things the same in the other browsers that ARE working.
That's the issue with these emulators. They basically 'display' the layout, nothing more. And to answer your question browserlabs is free. Just need an Adobe ID.
Another solution is buy a cheap laptop or old desktop and install the other browsers. That way you have a separate test machine ad it shouldn't cost you more than $200. You don't need anything fancy(big had drive, lots of RAM, etc.). Just a plain vanilla machine for testin.