I am in the process of redesigining our organisation's website and I wanted to put up boxes with rounded corners. There are so many ways to do this but I wanted to use CSS with images. A search on the web led me to so many resources.
The best and the most easiest is RoundedCornr. You have the option of a Basic box, boxes with a colour gradient, with border or one with several options. ALl you have to do is decide the colour, corner radius, etc. Press the "CreateRoundedCornr" and you will have the code and associated graphics ready for download.
See an example here. I created the blue box with gradient using RoundedCornr.