Inventory select script?

I have been working on this for a couple of days now, and of course I have been searching the forum and google before asking this question. I am trying to build an inventory selection script that allows me to do the following:
-When the player collides with an item (a weapon) the item is added to the inventory.
-Once one or more items are in the inventory they allow the player to draw this weapon (IPO driven action)

  • If an item is not yet in the inventory the next item is automatically selected.
    For example.
    The player has access to a total of 5 different weapons. The player has only picked up 2 of these weapons. I want to be able to toggle between the 2 weapons using a single keystroke for each time you toggle. Plus be unarmed as well, being able to skip over the 3 weapons that the player has not yet picked up.
    I hope I have explained this clearly enough.
    Thank You