If you really need to reach Opera, iCab and Netscape 4.x surfers, it is best to stick to conventional table-based layouts and use CSS only for specifying type within the table cells. Netscape 4.x is too long in the tooth to worry about and getting rarer by the day, but the other two are current versions and really should be able to render CSS a lot better than they do.
CSS gives designers many new possibilities, and lots of new headaches. Its advocates say that it is the way of the future, and I don't doubt that for a minute, but things don't change overnight. Surfers don't jump on the latest browsers as soon as they come out the way designers do. Some don't have the choice, some don't know how and many don't care. In the end, the Web is about communicating and it is your job to get the message across in the best way you can for your intended audience.