Best way to save file in folder?

ASP.NET/VB.NET
I want to programatically store a .txt file containing a user login and password in a particular folder.
However I want it encrypted so that no one (apart from one of our aspx pages) can read it.
How would I do this (encrypt and write the file after prompting the user for it once, and also unencrypt and read it at a later point) using ASP VB.NET?
TIA
Mark

P.S. I have the following code from http://www.freevbcode.com/ShowCode.asp?ID=4492 but it still needs to be encrypted: 
Public Function GetFileContents(ByVal FullPath As String, _ Optional ByRef ErrInfo As String = "") As String Dim strContents As String Dim objReader As StreamReader Try objReader = New StreamReader(FullPath) strContents = objReader.ReadToEnd() objReader.Close() Re ...