You can use Notepad++ which is a very good free text editor.
From its "Search" menu go to "Replace" and then in the "Find in files" tab.
Type the text you want to find and the replacement text, and specify the file mask for the files to be searched.
Microsoft has also a tutorial to show you how to create a vb script to do this job
http://www.microsoft.com/technet/scriptcenter/resources/qanda/feb05/hey0...
Does it support UTF-8?