Ok, here is the problem
MS Excel allows me to save the whole sheet as text tab delimited
I’m using this text in a program , but the user needs to make the previous step manually
I want to automate this step so the user only import the Excel Book into my program , and shows how many sheets inside it letting the user select the desired sheet and then the program will convert this sheet into text (tab delimited ) , any ideas ?

Well… one of the easiest to learn methods would be the use Excel Interop. The downside of this method is it (1.) requires Excel to be installed and (2.) Can get messy very quickly… but generally it makes sense.
I suggest familiarizing yourself with Excel Interop. Now, take note of the SaveAs method for the Workbook object.
Hope that helps. Just remember, it’s doable.