Unix Security and auditing

I am starting an audit of unix security within our company and am looking for any information that may assist me with this. I am looking for any tips or pointers that I should be aware of when looking at unix. I am very new to unix so any help will do. Maybe there is someone out the that has had some audit experience on unix. Thanks.

What distribution and version of unix are you using?
Can be helpfull in providing relevant links.

As far as I know it is HP Unix

Some possibilities:

SAINT: http://www.wwdsi.com/saint/
Tara: The Advanced Research Corporation ®
Tripwire:
Open Source Tripwire® download | SourceForge.net