How Can I Replace the First Five Characters in a Text File With the First Five Characters in the Computer Name?

Hey, Scripting Guy! How can I open a text file and replace the first 5 characters with the first 5 characters of the local computer name?-- EC Hey, EC. You know, you might find this hard to believe (his fellow Scripting Guys absolutely refuse to believe it), but sometimes the Scripting Guy who writes this column is all talk and no action. For ex...