From Eudora, easily open a message in your web browser, where it will be rendered properly.
Library folder under your home folder, make sure there is a Services folder. Create one if not.

The Mac Eudora we know and love (except for the glaring HTML problem) is being replaced with an opensource version that will use the same HTML rendering component that is found in the Firefox browser and in the Thunderbird email program.
Many thanks to waffle software, maker of the ThisService application, which made it easy for me to create this Mac OS X System Services item.