At least on Windows XP, Internet Explorer 7 uses an obsolete
(1987!) mapping table for the Greek encoding ISO-8859-7, namely
http://www.unicode.org/Public/MAPPINGS/ISO8859/DatedVersions/8859-7-1987a.txt

Compare the newer versions at
http://www.unicode.org/Public/MAPPINGS/ISO8859/DatedVersions/8859-7-1987b.txt
http://www.unicode.org/Public/MAPPINGS/ISO8859/DatedVersions/8859-7-2003.txt
http://www.unicode.org/Public/MAPPINGS/ISO8859/8859-7.TXT

This means that Internet Explorer 7 (at least on Windows XP)
does not display a euro sign at 0xA4,
does not show single quotation marks at 0xA1 and 0xA2 but
"modifier letter reversed comma" and "modifier letter apostrophe".

Look at
http://www.unics.uni-hannover.de/nhtcapri/greek.html7#symbols
under "euro sign" and "single quotation mark". Compare with
Firefox.

How is that on Windows Vista?