Is there a program to monitor file system changes?

As medium time lurker and first time Mac owner, I was wondering if there was a free program that will monitor what files are installed during an installation process and to monitor changes to files already on the hard drive? I figured because Mac OS has it roots in a BSD style system, surely there must be something out there, but I just can't find it. This is why I'm turning to the experts here to see if anything like this exists.

Thank for your help.

I really hate to bump my own thread, but I find it hard to believe that no one knows a program like the one I am looking for. Is there any hope here.

Please help, thanks.