Help with program

I have attached a zip to the post and I need help trying to finish this. The problems I am having are when I click the nextStudentButton and laststudentbutton it goes until the end of the array. I would like to get it to stop at the last name that is stored in the arraylist.  Then i also am having trouble when i am adding a student to the arrayList I want to be able to compare the idnumber of the student already in the list to the id number of the new student I am adding and if the any two id numbers are the same then the student cannot be added. Any help would be appreciated. Thanks

When I use either button- it moves to last name ?
As to check id try this

 public void checkId()
{
foreach (Student stu in students)
{
if (stu.IdNumber.ToString() == idAddTextBox.Text)
{
MessageBox.Show("Sorry.Student id already in use");
return;
}
}
}

Thank you for that code to compare if the ID is already in the array list.  They should not both go straight to the last name the lastStudent button should go straight to the last name but as for the nextStudent button it should display a different student every time until the end of the array list.  But what I am having trouble with is that when I click the nextStudentButton I can continue to click until the end of the array not the last student.  

There is a problem in your code - but it will take some time to work it out.
Soon as I get somewhere, I'll post result

Here is my idea on your project