I had to install openSSH, SSH in and edit an existing theme for the iphone. I cropped the Impossible is Nothing graphic, it looks really cool, and it is pretty easy. Just navigate to whatever theme you're using in you're iPhone's SSH (user name root, password alpine). You could use WinSCP or something along those lines. Just replace the background file and you're done.
oh! and it can be done via WiFi, no USB cable necessary, also, you can set it up to automatically sync via WiFi with some work. It's really neato, if I find the article to do it I'll post it. Click Me
It would have been funnier if you said Spring because technically it's a theme for the Springboard . Still, funny nonetheless.