// Initialize a new textbox
TextBox txt = new TextBox();
// Set the dimension and location
txt.Top = 10;
txt.Left = 10;
txt.Width = 100;
txt.Height = 25;
// Set the visibility and add it to the form
txt.Visible = true;
Save all the controls with their properties in a text file and load the control at runtime.....
I have attached a solution that uses a simple logic to create textbox at runtime. The program stores the no of textboxes created in a file. And on page load, reads the file and creates the textboxes.
This may not fit your situation but give u an idea on how to continue....
The attached file is just my way of implementing your idea. There are ofcourse many other effective algorithm available