VS 2010 Creating A Console Application That Will Create And Store Client Information As A .txt File?

Basically i am creating a console application that will create and store client information as a .txt file it is going okay but i have come across a slight hick up i want to use something on the lines of this .....

dim lastname as string
Do Until Integer.TryParse(Console.ReadLine(), LastName) = False
Console.WriteLine("Invalid input, Please try again")
Console.Write("LastName:-")

[code].....

this works fine to trap out numbers from letters but the problem i am getting is when the program calls uppon LastName it is recording 0 and wanted to know if there is a way of getting past this ..... so basically i need a way to allow letter but not numbers and symbols and then dispay a pernolised error message but at the same time use Stream writer to save was the answer is in a .txt file.