Checking the files installed by a package is easy enough with the Synaptic package manager (Right-click package > properties > installed files tab).
Here’s how to get that information without leaving the comfort (cough) of your bash terminal:
$ dpkg-query -L package_name
For example:
$dpkg-query -L flashplugin-installer /. /usr /usr/lib /usr/lib/xulrunner /usr/lib/xulrunner/plugins /usr/lib/mozilla /usr/lib/mozilla/plugins /usr/lib/iceape /usr/lib/iceape/plugins ...