Hi All :-)
just playing around with my twitter background today and realized that someone else might be wondering how to customize theirs too... so here's a little freebie to help you do just that,
you simply make a layout over the top of this jpg (its easiest to first put the background of your choice on, then make that layer invisible while you place the elements in the gray areas on both sides) The white area is where the twitter posts go :-) Then all you need to do is turn the background paper back on, turn off the template layer and save it as your twitter background (i've included instructions on it for how to add it to your twitter page too :-) I hope you enjoy it!
You can download it HERE
Have a Great Day!