Becky,

I've never used the EasyMod module that you reference in your post, but to change a skin's background you generally would need to modify the skin file & probably a CSS file too. Usually the skin file is a .ascx file that is named similar to your skin and the CSS file is something like "skin.css".  

If you're not familiar with how "skinning" works you should reference this video.  There are also a lot of videos available to walk you through various aspects of maintaining a DotNetNuke site on the Video Library page. 

When adding a module to the page you will have the options of different "panes" to place the module into. The panes are created / reside in the skin file which is usually created by the designer or front-end developer.  Typically a site would have something like a "Top Pane", "Left Pane", "Middle Pane", "Right Pane", and "Bottom Pane", but I've seen some skins with more than 25 panes in them.  The pane you place your module in is up to you, but you can always move it again after you've placed it into a pane via the settings.  If you view your page in "Layout mode" (depending on your version this will be somewhere in the top-right hand corner area) you can see the layout of the panes that the skin designer has created. This may help you in selecting which pane to put the module in. Also keep in mind that you can have multiple modules in the same pane. This is a common practice as well.

Hope this helps!