center page content
This will only work if the DOCTYPE is XHTML Transitional or Strict. IT WILL NOT WORK if your doctype is HTML 4.x. Here is an example of what it should look like:

Put this at the top of your CSS file and you will be good to go!
#html, body {
top: 0px;
right: 0px;
bottom: 0px;
left: 0px;
height: 100%;
margin: auto;

there seem to be many approaches these days for blocks with rounded corners.

there was one fully CSS version that draws one line rows along the top and bottom of the block with margins to give the rounded effect:

The rest use 2-4 images to get the effect
rounded corners css - Google Search
25 Rounded Corners Techniques with CSS
Spiffy Corners - Purely CSS Rounded Corners