I'm not sure which episode is this, but its pretty epic. Was shown last night at Nikki though. There's another epic throw in Asahi VS Ojima. Can't find the pic though.
There are some wallpapers at the fanclub website if you are a fanclub member.Or just create one yourself
AFAIK there are only 2 options for official wallpapers: 1280x1024 or 1024x768.