I didn't ask what path you were using, I asked what code you were using.
You should be using one of the getResource methods from Class, such as Class.getResourceAsStream.
Exactly where is the file? (Oh, I see it now, you have it at D:\\Project13\\src\\config\\appconfig.xls) You originally said it was at D:/Project13/sonnetframwwork1/config, so I assume the full path would be D:/Project13/sonnetframwwork1/config/appconfig.xls. But since Sumit's suggestion didn't work, I suspect that the file is not there.
Is the XSL file in the JAR file? Or do you intend to have the file be external to the JAR? If you have it external to the JAR, I recommend using a system property to identify the location of the XSL file, and if none is given to use "appconfig.xsl" as the default path, which would mean that it is in the current working directory.
By the way, when you run Ant, which directory are you in? Are you in D:/Project13/sonnetframwwork1? If you are not in d:/Project13, then the path of "src\\config\\appconfig.xls" will not work. Relative paths are based on the current working directory.