Most Halloween desktop wallpapers are based on all the usual clichés - scary ghosts, witches, ghouls, etc.
The simply-named Halloween Wallpaper does feature a pumpkin but it's an altogether more tasteful look. Halloween Wallpaper is a collection of pumpkin lanterns based on a black background with a cheery "Happy Halloween" message. It's only available in one resolution though which is 1024x768 pixels.
If you're looking for a desktop background that avoids all the usual scary cliches this Halloween, Halloween Wallpaper fits the bill.