Use Powershell together with a scheduled task to change backgrounds periodically. It’s up to you and you never know what’s coming next! You tell it where to get pictures from and how to show them – maybe you just want to see one photo at a time or maybe you’d like to see a ‘Snapshot Scrapbook‘ of photos thrown across your desktop. JBS sits in your system tray (down by the clock) and changes your background at the time interval of your choosing.
Since Microsoft limits you, your best shot is to use a third-party tool like John’s Background Switcher Notice that the desktop background slide show is not available in Windows 7 Home Basic and in Windows 7 Starter.