If you want to add a virtualhost on your Mac OS X box without having to wait around for ages, then the easiest way to do so is to shove a line into /etc/hosts and flush the dnscache. Here's a friendly bash function to throw into your .bashrc:

function edithosts {
	if [ -x "`which $EDITOR`" ] || [ -x "`which $1`" ]
	then
		if [ -x "`which $EDITOR`" ]
		then
			export TEMP_EDIT="`which $EDITOR`"
		else
			export TEMP_EDIT="`which $1`"
		fi
		echo "* Using ${TEMP_EDIT} as editor"
		$TEMP_EDIT /etc/hosts && echo "* Successfully edited /etc/hosts"
		lookupd -flushcache && echo "* Flushed local DNS cache"
	else
		echo "Usage: edithosts [editor]"
		echo "(The editor is optional, and defaults to \$EDITOR)"
	fi
	unset TEMP_EDIT
}

More simply, you can just flush the DNS cache manually with:

lookupd -flushcache