I am trying to download the latest version of safari onto my MAC but, it's telling me I need to download all these pre-requisites... What do I truly need in order to download safari 5.0.5? I have Safari version 4.0.3 and Softward 10.6.8.

Not knowing what version of OS x you are running and what updates you have applied you may have to download some additional updates to install the latest Safari. The latest OS 10.6 update is 10.6.8 if you are on 10.6 you should be there.
Updates are a good thing to run, they fix, none issues, and security concerns. You should keep your computer up to date.