That forum is using vB3.7, so it's a bit different than vB4. You can still make your forum look like that, but probably not exactly like that. It's really only a matter of changing your style/templates. You may want to start here with Don's blog entries and download the StyleVar Dictionary and the Skinning guide:
vB4: Skinning Your Forum in 10 Easy Steps and
StyleVar Visual Dictionary for Forum, Blog, and CMS (PDF Documents)