There is no automatic mechanism for converting a .txt file to XML in any language. You have to define the XML schema and then write the code to generate the XML file. You could also read in your text file into some form of structure and then use the Flatten to XML functions to use the NI XML schema. If you need to use your own XML schema then you would need to use the XML Parser VIs to generate your XML file. Alternatively, you could use LabXML or JKI's EasyXML Toolkit.