To be extra sure you don't lose some settings, you could also back up the registry entry at -
HKEY_CURRENT_USER\Software\JRiver\Media Jukebox\View Info
(I think that's all you need , but I'd also back up the whole HKEY_CURRENT_USER\Software\JRiver\ key just in case)
PS: Plugins such as AlbumView may store their setup info in different area's... this just covers the main library and your column layouts.
PPS: You should copy whole Media Center/Data directory somewhere safe (this directory stores your library, backups, thumbnails, and maybe your cover art).... [size=-2]...oh, and if you -really- want to be safe, you could then burn it onto 13 cd's and post 12 of them out to friends, preferable half in other countries, and lock the 13th in the fireproof/ultra secure 15m thick double reinforced adamantium safe at the bottom of your bomb shelter/underground city block... [ well, maybe that's a bit much, but at least it'll be safe... wait, you probably need one copy off planet too... just to be sure :) ][/size]
[size=-3]Edit: January 06, 2004 - slightly more rewording (removed paranoia) :)[/size]