Is there a way to use dynamic wallpaper with xml files? Thanks

You may need to write your own wallpaper plugin to achieve this. What exactly are you trying to achieve?

I was on gnome 2 before and I got a wallpaper changing with the time of the day with a xml file, like this one: http://www.omgubuntu.co.uk/2011/04/this-neat-wallpaper-for-ubuntu-changes-with-the-time-of-day/

You can display a slideshow as the background, but I'm not sure it is configurable enough for your needs.
Under desktop settings, you have different options for the wallpaper, slideshow is one.

you could look at wally though it changes wallpapers on an interval not a time of day basis http://www.becrux.com/index.php?page=pr ... name=wally http://kde-apps.org/content/show.php/Wa ... tent=98455