You can post information about the eMac to inform us of the model, in order to assess its capablility and how high it can go OS wise.
Click on About this Mac, More info, and look at the hardware overview.
if it is not running, you will be able to get a few clues about it from this site.
You must use retail install disks for Tiger to upgrade (black with a big "X"). The grey system install/restore disks tha shipped with another Mac usually fail, and the grey diskd shipped with an Intel Mac always fails.
Most Tiger retail disks are on DVD. Many earlier eMacs shipped with only CD or CD-R drives. That's been a problem for upgrading in many cases.
If the computer is not running, you can determine the variant you have from this Apple article: