This comes courtesy http://www.cyberciti.biz/tips/lighttpd-redirect-www-domaincom-to-domain-com.html
For various reason you might want to redirect all traffic coming to www.domain.com to domain.com or vise versa.
This is essential if you want to maintained good structure for search engines (SEO) or to generate accurate stats.
Open your /etc/lighttpd/lighttpd.conf file:
# vi /etc/lighttpd/lighttpd.conf
Find your virtual domain section.
h4. Add following configuration directive if you want to redirect www.domain.com to domain.com
$HTTP["host"] =~ "^www\.(.*)" { url.redirect = ( "^/(.*)" => "http://%1/$1" ) }
h4. Add following configuration directive if you want to redirect domain.com to www.domain.com
$HTTP["host"] =~ "^domain\.com$" { url.redirect = ( "^/(.*)" => "http://www.domain.com/$1" ) }
Close and save the file. Restart the lighttpd web server:
# /etc/init.d/lighttpd restart