The first Microsoft operating system with ISO-8859-13 support is Windows XP SP2. It means that the first Outlook Express version that supports this encoding is 6 SP2 (SP2 for IE and OE is a part of SP2 for XP and is not available for older Windows versions). While it is possible to manually change encoding to Windows-1257 (Windows Baltic, this encoding is a near exact superset of ISO-8859-13), it is a bit awkward. Experiments have shown that it is possible to add partial support for this encoding to Windows 2000.
Adding support for ISO-8859-13 requires making some changes to the system registry. They pose no danger to the system provided they are done correctly but I strongly advise you to update your emergency repair disk and make sure you know how to use it. Thanks to these changes you will get partial support for ISO-8859-13 in IE 6 SP1 (tested with version 6.0.2800.1106) and OE 6 SP1 (tested with version 6.00.2800.1807)—IE is able to display correctly all extended characters on web pages using this encoding (provided it was correctly declared), OE is able to display correctly all extended characters in messages using this encoding (provided it was correctly declared) and to reply using ISO-8859-13 to a message that was encoded using this encoding. However there is no possibility to manually change encoding to ISO-8859-13 in any of these programs. As a bonus, it is also possible to use this encoding in the console. In the MS parlance, this encoding is confusingly called “Estonian (ISO)” even though in Estonia the Western European ISO-8859-1 encoding is used more often (Estonian is not a Slavonic language, rather it is related to Finnish). Usually this encoding is called “Baltic” or “Baltic Rim”, it is an official encoding in Lithuania (Government standard LST ISO/IEC 8859-13).
You will need to get a c_28603.nls file. This file is included in the installer of the ReactOS 
—an open-source operating system that can be downloaded and used by anybody for any purpose. Another source of this file is the Windows XP SP2 setup program or the SP2 (please remember that if you just download this file from the internet or copy it from your friend’s machine, you will be braking the law). You will also need to make some simple changes to the registry.
Below you can find contents of a .reg file that will automatically add all the enties above. You may copy it all to Notepad (do not omit the empty lines at the end, otherwise it won’t work), save it with a .reg extension and double-click it.
Here’s illustration: Screenshot of IE 6 SP1 displaying a web page encoded in ISO-8859-13, with charset selection menu, screenshot of OE 6 SP1 displaying an e-mail encoded in ISO-8859-13. OE’s title bar shows encoding used.
It is possible that the procedure described above can be applied to Windows NT4 and Windows 2003 Server but I am unable to test it. I give no guarantees whatsoever about the procedure described above. I have tested the procedure and encountered no problems but I accept no responsibility for any problems, loss of stability, loss of data, etc. Any breach of law due to unlicensed use of the c_28603.nls file taken from Windows XP is the sole responsibility of the person using the file.
After applying all the changes described above it is possible to change encoding used by console in windowed mode: just type CHCP 28603.
As an aside, it is also possible, using the above described method with small modifications, to add the ISO-8859-16 to encodings supported by the console window. The MS code for the encoding is 28606, the required file’s name is c_28606.nls and only the registry entry relating to the key HKLM\…\NLS\CodePage is required. The command to change console encoding to ISO-8859-16 is CHCP 28606. This addition will not result in adding support for this encoding to IE or OE, though.
The procedure was tested on Windows 2000 SP4 English, all updates current as of November 2006, IE 6 SP1 6.0.2800.1106 and OE 6 SP1 6.00.2800.1807.
