There is a great little freeware app called OSXPM Package Manager
which serves as a package manager for OS X. Basically, you can use it to install and uninstall packages, or look inside them to find exactly what is installed and where.
A word of caution though - be careful what you delete! I've been running a pre-release of QuickTime 6, but for a number of reasons decided to go back to 5. So, I thought, I'll use OSXPM to unistall the package.
Bad move. QuickTime is, as many of you will be quick to point out, an integral part of OS X - so by removing all components of QT6, I effectively screwed OS X. I couldn't even start up (it hung half way with a blank blue screen).
However, it was OSXPM again that came to the rescue. Not wanting to reinstall OS X on my main drive (I didn't have time!), I did a clean install on another drive. Then, using OSXPM, I checked exactly what was in the QT6 package (and therefore what it deleted). I then copied all these files from the clean install to my main system, rebooted, and presto! All working fine again.
So, in summary, OSXPM is a very useful app, but be careful what you do with it!