Each application now has it's own configuration file. To enable <code>write18</code> run
initexmf --edit-config-file=miktex\config\pdftex.ini
or (if you have MikTeX 2.5 or a version of ConTeXt from 2006)
initexmf --edit-config-file=miktex\config\pdfetex.ini
and put
EnableWrite18=t
into it. An alternative is to se the environment variable <code>MIKTEX_ENABLEWRITE18=t</code>.
''Note: it could have made more sense if MikTeX would read settings from pdftex.ini, not from pdfetex.ini in 2.6. I don't know if this is intentional or not though.''
=== Linux/Mac ===