There are a lot of different logs and so on that you can use. Most have either too much detail, or not enough, or only log errors.
You can find them in:
/Library/Logs
/var/log
You might also check the Installer log:
Go to Applications -> Utilities -> Installer
Cancel out of the Open package dialog that comes up
Choose File -> Show Log.
You can also check the software update log in the Software Update preference pane.