The only way I've found to make rounded corners is to do it by creating eight tiny graphics, and putting them round the edges of a 3x3 table.
topleft, topcentre, topright,
middleleft, middleright,
bottomleft, bottomcentre, bottomright.
* Make sure that the height and width of each corner graphic match, and that the height of the top and bottom graphics, and the width of the left and right graphics also match accordingly.
Make the cell properties as follows:
topleft: width=1%, height=1%
topcentre: width=98%, height=1%
topright: width=1%, height=1%
middleleft: width=1%, height=undefined
middlecentre: width=98%, height=undefined
middleright: width=1%, height=undefined
bottomleft: width=1%, height=1%
bottomcentre: width=98%, height=1%
bottomright: width=1%, height=1%
Put your content in the middlecentre cell.
Put your graphics in the correct cells around the edges, and make the background properties of the topcentre, middle left, middleright, and bottomcentre cells also to be the graphics that are in the same cells respectively.
Make the table properties to be borderwidth=0, and cellpadding=0 and cellspacing=0. Table width can be whatever you want, but the height should be undefined (unless you want the height to be larger than the amount of text in the middle centre cell for some reason - leaving it undefined will allow the table to stretch vertically depending on the amount of text in the centre cell).
Have fun!
Pete