Unfortunately, as of OpenBSD 4.0 there isn’t a standard package for PHP with FastCGI support.

cd /tmp
tar xzf /tmp/php5.1-with-fastcgi-openbsd-4.0.tar.gz
cd /tmp/php5 && make install clean

…wait a long, long time…

Install Subsequent PHP Support Packages
pkg_add -v /usr/ports/packages/i386/all/php5-mysql-5.1.6.tgz
/usr/local/sbin/phpxs -a mysql

Example /etc/lighttpd.conf For PHP
$HTTP["host"] == “www.<example>.com” {
   server.document-root = “/www/sites/<example>.com/www/”
   index-file.names = ( “index.php” )
   server.error-handler-404 = “/index.php”
fastcgi.server = ( “.php” =>
   ( “localhost” =>
      (
         ”socket” => “/tmp/php-fastcgi.socket”,
         ”bin-path” => “/usr/local/bin/php-fcgi”
      )
   )
)
}

Example /etc/lighttpd.conf For Ruby on Rails
$HTTP["host"] == “www.<example>.com” {
   server.indexfiles = ( “index.html” )
   server.error-handler-404 = “/dispatch.fcgi”
   server.document-root = “/Rails/public”
   fastcgi.server = (”.fcgi” => ( “<example>” =>
      ( “min-procs” => 1,
         ”max-procs” => 5,
         ”socket” => “/tmp/rails-<example>.fastcgi”,
         ”bin-path” => “/Rails/public/dispatch.fcgi”,
         ”bin-environment” => ( “RAILS_ENV” => “production” )
      )
   ))
}

Start Daemon on Server Startup, Add to rc.local
if [ -x /usr/local/sbin/lighttpd ] ; then
  echo ‘Lighttp’
  /usr/local/sbin/lighttpd -f /etc/lighttpd.conf
fi