Yeah. I think the Prismic program only worked for a very short time.

However; You could do it manually by searching for (replace the search phrase):

Google image search 3200x480

Slice them up in four parts (assuming that's the number of desktops you use on your phone)

If you don't find enough options, I would go to search for 800x480 and combine.

Google image search 800x480

Use a .desktop file as described here

http://wiki.maemo.org/Customizing_Maemo#Wallpapers_2