I would use genke's information to get the value into a variable on the left side of the equal sign. After that is working you can look up code for how to write to a file.
I think it is done with the FileSystemObject. Is that the right name folks?
You open or create a file. Then append to the end of the file. There are a lot of examples on line. I usually look at my VBScript book or one of Tarun's wonderful books to remember how to do this.