Homework, eh? There are many books written on it.
Start with WIKI
and take a look at this white paper
on wireless security.
The bottom line is if you really want a highly secure network, no Internet access, no wireless, strong user authentication and site security, no ability to copy data to any devices (so no outside email, no USB sticks, no floppy/cd/dvd/etc.). Then compare that to the "average" home user that still uses WEP or nothing on their wireless.