Square corners seem to be "like totally out" as far as web sites are concerned. Rounded corners are not too hard to do. You use a program, such as Photoshop, and design four corner images for the north-east, north-west, south-east and south-west corners of the box. Then setup some CSS styles to go along, and you are set. Easy enough, but it is still a pain. I happened upon a very interesting technique for doing this, written by Alessandro Fulciniti. This article is from back in 2005, so it obviously not a new technique, but very cool none-the-less!

Using "Nifty Corners" you can easily create CSS styles that make use of no images at all. This is much easier, and will create web sites with much faster loading time. It uses a mixture of Javascript and CSS. I may make use of some of this on my site.

http://webdesign.html.it/articoli/leggi/528/more-nifty-corners/1/