how to generate sequential number?

Question

I have seen only the random number generating trick over the net but could get nothing about sequential number generating idea. I think it is easy but hard for me, therefore Pls. reply me how to write code in visual basic 2010 for: If there is two textboxes, one is for low value and another is for High value and another button is generate command. Another one listbox is for output value appearing.There the output value must be appear within a second by using timer counter. Finally the listbox items must be saved as text file. How to write code for this purpose pls help me......