Scribus application won't open

[kakapo]

hi, just downloaded the Scribus_1.4.0.rc5.tiger_intel.dmg onto my macbook running OSX 10.4.11.
unpacked an put into Applications folder - BUT it will not "open" - please advise!?

I successfully downloaded one for windows environment and it works fine - but strange that the dmg for that was only 20meg versus mac version 140meg - another question - as I am based in Vanuatu with a very very slow connection. it took 3 hours to download the mac version!