After you drag and drop a web part onto a SharePoint site, you have the ability to modify the look and feel via the shared web part properties. One such property is Chrome Type. It allows you to set the appearance of a specific web part to have Title Only, Border Only, Title and Border, or None. The default setting is Title Only. What if you want to change the default for all your web parts?
First, some educational details. The Chrome Type is actually associated with a web part zone (or section of a SharePoint site). It determines the default presentation for all web parts in the zone. Via shared web part properties, the default can be overridden for a specific web part. So, where are the web part zone defaults stored? These are located in the site templates directory (../program files/common files/Microsoft shared/web server extensions/12/templates/sitetemplates/../XML) and are in the onet.xml file. You’ll see an attribute called ‘ChromeType’ for each zone in the site template. There are about a dozen site templates. So, to change the default for all sites that use a particular site template change the onet.xml file.
The available values for ChromeType are here:http://msdn2.microsoft.com/en-us/library/system.web.ui.webcontrols.webparts.partchrometype.aspx.