Designing for browser compatibility?

[jwoolf09]

Help needed, please:

I'm working on a website for a friend's small business. I'm also using it as a self-training exercise. I want it to be a nice website using as much nifty stuff (CSS2, a bit of Javascript, absolute and relative positioning, layers, tab-buttons, that sort of thing) as I can manage, but I want to minimize any risk of using features that common browsers won't be able to recognize and render correctly. So I'm wondering what level of nifty stuff I can safely use.

I already know that Firefox 1.5 and MSIE 6 don't always render CSS-formatted pages the same way, which is a friggin' nuisance. A check of my own website's user logs shows that for this year, about 88% of the non-bot hits have come from browsers that should be CSS2 compliant: Firefox, IE6, IE5, Mozilla 5. IE6 accounts for 71% of all visitors, all by itself. The two names in the top ten list that concern me are Safari (no version information given) and Opera 8.5. I know nothing about either one. How reliably CSS-compliant are they?

What level of browser do you folks design for? How often do you get user complaints about browsers that don't render CSS websites correctly?

-- JSW