If you’re trying to use the Text Image Generation for Windows, you need to download the Text Image Generator executable (http://testplant.com/downloads/WindowsTIG.zip) to the Windows machine, install it, and start it running.
If you’re trying to use it to test a Mac, then you’re seeing some other problem, so let us know.
For examples, see pages 16-22 of the Using Eggplant manual.
If your app isn’t using default fonts, your developers should be able to tell you what fonts they specified. This should be part of the deliverable.
If you can’t get that information from them, then you need to resort to guessing. We hope in the future to be able to provide some means of extracting that information from the SUT.