Ok, I recently finished downloading the Setup(took about healthy 5 hours, let computer stay on overnight) but when I tried opening it with WinRAR error pops up saying 'DBO_TW_setup_20110922:unexpected end of archive'

I tried ignoring it and then trying to extract the files but then the same error pops up along with
'DBO_TW_setup_20110922:The archive is either unknown format or damaged'

So did something go wrong with downloading, am I using the wrong program to open it, should I try redownloading it or what?

It's a shame since I got all Wasabii accounts and such ready just for this and I'm
really looking forward to playing this seemingly great game.
(Been a great fan of DB series ever since they started publishing the mangas here about 7 years ago)

Where did you download it?

From here, used the direct download link.

Edit: I'm downloading the Torrent as we speak. hopefully it works perfectly (just 30 mins. left)

Redownload, try the torrent download from the wasabii site itself. It's much faster, the link from dbocom is a bit old.

http://dbo.wasabii.com.tw/DB_Download/client.shtml

Use utorrent to download.

Yes! This is much better. everything is in perfect working order.

Thank you very much.