there are several existing threads about demonoid invite
also,if you just need to download one file from demonoid, post that name of the file you need. maybe someone can download the torrent file (which will be less than 500kb) and send the file to you
the only private thing about demonoid is the site itself. the tracker is not private, anyone can use the tracker, even if you are not a member of demonoid so as long as you have the torrent file, you can download from demonoid