First, find a quiz that you think you would like on iQuizr.com, or make your own. Then, click on the "Download This Quizpack" link.
When you click the download link, you should receive a pop-up box asking you what to do. Choose a location on your computer to save the file and click "OK". I recommend downloading the quizpack to your desktop - where it is easy to find it for the next step.
After the file has magically transmitted to your computer, the quizpack will be in a zipped format. Unzip this file using an unzipping application. The result will be a quizpack folder.
More or less, you need find the directory that houses all your iTunes content. In Windows, the iTunes directory is locaed in the "My Music" folder (in "My Documents"). On a Mac, the iTunes directory is simply in your home ~/Music directory. If you have downloaded the iQuiz game from the iTunes music store, you will see an "iPod Games" folder inside the iTunes directory. And within the "iPod Games" folder will be "iQuiz 1.0." The iQuiz folder is where all the quizpacks are stored for the iPod. Simply move the unzipped folder from step 3 into the "iPod Games" folder.
NOTE: These quiz packs will only work if you have downloaded "iQuiz" from the iTunes Music store.
Open iTunes. Sync your iPod like normal. When you are finished you should see any new quizpacks when you start the iQuiz game on your iPod. Enjoy!