put it up here and then follow the instructions:
it's not something that was downloaded onto the computer. it's an option in the desktop/display in the control panel. can you even copy that stuff?
yep! in there, click on the wallpaper in the list, then hit the Browse... button. You'll see the file. click it and hit CTRL-C (or right click and hit copy). then Paste it onto your desktop for easy uploading.