The reason you use autonumbers and link that number is because it is unique. Take names for example, if you had John Smith customerID 1 and it stores the 1, at this point it doesn't really matter which value it stores, the text or the number.

A few days pass and you get a call from someone in the next town over, but his name is John Smith too, now you'll have to put him into your database and he becomes CustomerID 2. Now when you go to refer to John Smith all of a sudden there are two John Smiths, with no way to tell which one is the one you are talking about other than the unique number. So when you go to open the customer information for John Smith, maybe you get John Smith A or maybe you get John Smith B if you store the text, you would always get customerID 1 or 2 though if you store the number. John Smith isn't unique so it shouldn't be stored as a relationship primary or foreign key.

Expanding on Adam's example the ID is the one thing about a person or thing that will never change.  #1 John might move 6 months from now but remain your customer. He might get a new phone number, change jobs, get a new car but he will always be Customer ID 1.  
If you change his information you don't want to have to change every other record you have for him.
  
It is also much more efficient to just put in an ID, for an order say, than to enter the full information about that person each time you enter an order.  It reduces errors and duplication / redundancy.

This is also why we say, "Autonumbers are not for you".  Once used, it is never reused and never repeated.
If you delete #1 John and reused the ID 1 for George Appleby then all past related records would erroneously be changed from John to George.

While we're using names as an example, this also applies to items on an order, appointments with a client, payments on an account, and on and on and on.  The ID is the link between two things. How one thing is related to another.  That is where the term Relational Database comes from.

William, am I understanding your question correctly, that you can't get the name to show up in a combobox while at the same time storing the ID in the table?