Creating a CSS web part? (hiding the right column on certain pages)

a) Overriding the layout with inline css works fine. WP in these special pages can hide the right column and stretch the first and second.

b) conditional css and adding special class with javascript is even better, IMHO

consider this:

<div id="wrapper">
  <div id="left"></div>
  <div id="middle"></div>
  <div id="right"></div>
</div>

Then css it like you want 290 pages of 300 to look like.

Then css the special 10 pages:

#wrapper.special-case right {
  display: none;
}

In wepbart or or in some element which the special 10 pages have in common, add the class "special-case" to the wrapper.

jQuery("#wrapper").addClass("special-case")

If,

1. There is a patten for these 10 pages which could easily distinguish them from the other 290 pages, and
2. There could be more pages want to hide the right column in the future, and
3. You hat repeating works.

Then, I suggest you use jquery in the master page to find out the 10 pages (maybe more pages in the future) and give them the css attached. This is an once-for-all solution, and, this is one of the reasons why we need a master page, right?

Else,

1. Create a webpart to generate the css and then put it in the 10 pages would be an ideal choice, since you can easily update the css and enable or disable it by just deploying the webpart solution in one place. So, you don't need to go through all the 10 pages to update the css style each time.