All applications, preference panels, info windows etc. should automatically adapt their layout to changes in system font size. Not necessarily "live", but after restarting the application. If anything doesn't change its layout accordingly, it means that there's a bug in need of fixing.

For this task you'll have to set the font size in the Appearance prefs first to 8 points, check every app, prefs and all the system for incorrect layout, alignment and drawing etc. Then do the same with 18 point fonts.

You could also change the font family.

Don't forget to restart Tracker and Deskbar after changing font size/family. It may be easiest to sjust quickly reboot...

Make a list of the tested components, document your findings also with screenshots.

Check out the user guide first when you're new to the system.