Last night I had an idea of changing my twitter background to a customized one. So I made one and put as beta. It was the worst ever twitter background I have ever come across. So googled for some help and found these useful links which thought I could share with you :)
http://www.fuelyourcreativity.com/free-psd-twitter-background-template/
http://www.creativepro.com/article/design-unique-twitter-background