I uploaded a Twitter background image to my profile. Here is what it looks like on my screen.

RustyBrick & Search Engine Roundtable Twitter Design

I used an old PowerPoint presentation background that looked like this:

RustyBrick & Search Engine Roundtable Background

I had to move up the "Search Engine Roundtable" piece to the top right of the design, to make it visible on Twitter.

I love this PPT background template.