You know why this works? Because you are starting a process to open up the text file which launches the program associated with txt files, probably notepad. It then passes a print command to it. So it is opening up notepad and calling print.
However this is not the standard way for printing and .NET does it much better and nicer. To do it you will have to look to your toolbox for the printDialog control and the printdocument control, adding both to your project.
Your printdialog control will be for the dialog screen where you can setup printer settings like landscaping or portrait. Once you got the settings, you would set the printdocument control's printsettings property equal to the printdialog printsettings and handle the printdocument's printpage event for sending data to the printer.
Below is a great site I found which will show you a bit of the code behind this. The example also includes a pagesetup screen and print preview so you can leave those out if you want to keep it simple.
Printing in VB.NETEnjoy!
"At DIC we be printing code ninjas!"