UPDATE!
The recent release of
MyBB 1.4.5 included a change to
functions.php. Please use the new version in the first post to overwrite the default
functions.php when you upgrade your MyBB installation.
@ghazal: Thanks for your support

Historically the original thread was based in 'Plugins - Discussion and Support' but the 'Tutorial' section is very appropriate too.
@Miley: Thanks for your feedback and PM. As suggested in my reply, the banner issue appears to be a result of the banner being wider than the CSS setting for #container (800px vs. 745px); the images also appear to be displaying correctly.
As for the font/text not displaying correctly (as per your PM - where the font for the User CP is white, which does not show up against your white bg) the workaround appears to be this:
td.tcat td.menu_row a:link,
td.tcat td.menu_row a:visited,
td.tcat td.menu_row a:hover,
td.tcat td.menu_row a:active{
color: #000000;
}
Hope this is helpful