You cannot access files you've placed in the project using the FileInfo object. Instead you create a Uri to access it.
Its not clear from your question which project you've place the file
in. If you have placed it in the Silverlight project then it ought to
end up as content in the Xap where you can use StreamResourceInfo to access it as follows.
StreamResourceInfo fileContentInfo = Application.GetResourceStream(
Also now the file content could be accessed as follows.
Stream fileStream =