This page used to contain advice about obtaining Greek fonts and configuring the browser to display them correctly in web pages encoded in ISO-8859-7.
However, since the time I first wrote it (1998), things have changed quite a bit, and I believe that nowadays most browsers support UTF-8 natively, and most operating systems ship with fonts that contain support for Greek, so things should Just Work.
If your browser has it right, the next line will be in Greek:
Αυτή η γραμμή είναι γραμμένη στα ελληνικά
(It says: this line is written in Greek.)