The essiest way to achive this is to change query_posts('showposts=1');
in your index.php file to query_posts('showposts=1'); so there will only show one post. Then you have to change the css, look for
#primary.twocol-stories .story{
float:left;
width:48%;
margin:0 0 0 4%;
display:inline;
}
and change it to
#primary.twocol-stories .story{
width:100%;
margin:0 auto 0 auto;
}
we set the width so it will fill the entire div and center it by setting the left and right margins to auto, not really necessary, but this will allow you to adjust the width.
If there are any images or otter things inside the post that have an specific width you have to change them in you css file.
I hope this will help.
Greetz,
Durgé
Dimics.com