Hi
1) Make a copy of your page.php file called page_wide.php
You can read this section about custom page templates
http://codex.wordpress.org/Pages#Creating_Your_Own_Page_Templates
if you care to
2) add this to the very top of page_wide.php:
<?php
/*
Template Name: WidePage
*/
?>
3) In the new page_wide.php, find the line for
<div id="left-column">
change it to
<div id="left-column" class="widepage">
4) In your style.css stylesheet, find this on line 47
#left-column {
float:left;
padding-left:40px;
width:500px;
}
Immediately after that section, add this
#left-column.widepage {
width: 775px;
}
5) Go to the WP editor. Open up any page you want a wide page on. To the right of the edit post box you will see a box for Template. Set the template to WidePage and save. Repeat for any other pages you want wide.
That should do it.