Aiwen, try installing from a DMG instead of something else. (There's no install procedure using a DMG, just a simple drag operation.)
Go to this page: http://wiki.scribus.net/canvas/Download
and click on "Mac OS X DMG
(Intel only, Leopard (10.5) or higher)" then, after you've been sent to the SourgeForge site and the DMG file has been downloaded, just open the DMG (double-click) and drag the Scribus icon from its window to your Applications folder.
You should now be able to open Scribus from your Applications folder.
Once installed, drag the Scribus DMG image (it looks like a drive icon) from your desktop to the trash to eject it. Just the Scribus DMG image though, not any other icon that looks remotely like a drive or you could cause yourself major problems.