I suggest using xelatex to typeset in Greek (or in Greek and English),
which uses Unicode.
If you still want to typeset with the grlatex format which uses ISO-8859-7, check: grlatexiso7/.
Here are some hints related to Greek and xelatex.
I have not tested them very much.
Simultaneous greek and english hyphenation in:
texlive (ubuntu) and miktex (windows)
Some of the following examples need fonts of:
Windows, Greek Font Society, Computer Modern Unicode, Libertine.
Examples and helper files