I uploaded new version. Rating is also added as custom field but maybe its useless if someone will use my script as the main script to gather movies info. 
	//orating
	i := Pos('<span class="average">', HTML);
	if i>0 then
	begin
		i := PosFrom('>', HTML, i);
		j := PosFrom('<', HTML, i);
		lStr := Copy(HTML, i+1, j-i-1);
		lStr := StringReplace(lStr, ',', '.', true, true, false);
		Log('Rating: '+lStr);
		AddFieldValueXML('orating', lStr);
		AddFieldValueXML('orname', 'Filmweb.pl');
		AddCustomFieldValueByName(cCF_Rating, lStr);
	end;
As you see, to custom fields you must use AddCustomFieldValueByName(fieldName, value) where fieldName is matched to field name in "Tools -> Preferences -> Movies -> Custom fields".