How to change the one column layout into a two column layout?

On the following page I have a two column layout which is great for my site and I love it:

http://simpleboutique.net/Category/1-formal-wear.aspx

For some reason other categories display a single column layout or flowlayout:

http://simpleboutique.net/Category/6-party-dresses.aspx

How can I change all the categories to use the two column layout?

Both of these categories has two column layout. Presume that you meant category template: go to category details page and change "template" property

You want the "products in grid" category template... that is what is being used in the category you like.

The "Products in Line 1" template is set by default when you add a category, that is what you have on all the rest of your pages. You must have changed the one for formal wear when you made it and didn't realize it.

B