Interchanging Wallpaper Theme

[Je5]

Ok a while back I found a theme on this site that had a interchanging wallpaper in the theme...
I am wondering how to make one or adjust a theme I already made with an interchanging wallpaper...How would I do it...I am on a mac and was wondering if I would make a plist for it or how else would it know to change the wallpaper...

[lach]

"do you want a interchanging background on the springboard?
this involves a html file. How many pictures did you want to have cylcing through?"

sorry, i mis read. How many photo's do you want cycling through on the springboard? have you made a html document for the theme?