We're almost there now - kids will be trick or treating, grown adults will be running around dressed as witches, and pumpkins will be being massacred all over the place.
Halloween Emoticons is a collection of five Halloween-themed icons to add a spooky mood to your Mac. They're all in PICT format with a resolution of 256 x 256 pixels. All the icons are based on a pumpkin though, so don't download them expecting other Halloween-related themes on your desktop.
To replace a generic icon with one from the Halloween Emoticons collection, CMD-click for the information dialog. Then copy the image to the clipboard, choose the Halloween icon you want to use and insert the new one. Alternatively, you can use an icon management program like CandyBar instead.
Halloween Emoticons are a bit misleadingly named - they're icons basically - but if you want pumpkin icons they're just the thing.