There was some dicussion on that here:
http://www.hiawatha-webserver.org/forum/topic/394
Here is a real-life example from my hiawatha configuration:
UrlToolkit {
ToolkitID = addwww
Match ^/(.*) Redirect http://www.daemonforums.org/$1
}
[...snip...]
VirtualHost {
Hostname = daemonforums.org
WebsiteRoot = /home/www/daemonforums.org
UseToolkit = addwww
}
VirtualHost {
Hostname = *.daemonforums.org, daemonforums.net, *.daemonforums.net, daemonforums.com, *.daemonforums.com
WebsiteRoot = /home/www/daemonforums.org
AccessLogfile = /var/log/hiawatha/daemonforums.org/access.log
ErrorLogfile = /var/log/hiawatha/daemonforums.org/error.log
StartFile = index.php
ExecuteCGI = yes
UseFastCGI = php
}