Eval Script for Magic Item set
 

Is it possible to write an eval script to define a pair of boots belt and cloak and tell the program what equipment slots these items take up?

Please explain exactly what you want here - do you want a single purchase, that takes up both the cloak and boot slots? That should be simple - just check the tags for both slots on the item. Or do you want the user to make one purchase, and get two items - boots and a cloak (and then be able to choose which they are actually wearing, and potentially lose or sell just one). That would be done with an auto-add.

The set takes the Feet slot/Boots, The Bel slot and the shoulders slot.

So you're looking to create four items, and you want to set the slots that each occupies?

I think we all need more detail on what you want to do.
The three items that you mention already have slots assigned to them. What do you mean by magic item "set"? Do the three items already exist in HL, or are these new items you will create? Can a Hero buy the items individually, or do they get all three together?

Dami the three items are a set that only function when together they can not be separated. They are three items a belt, cloak and boots. All I want to do is find a way to do is have the item slots filled when the items are equipped. I am not concerned with the items not functioning when separated I will just add that in the text for the sets description.

I am having another problem with the set I seem to have added something that changes the size of the wearer when the set is equipped it increases the wearers size by one size. I have no idea of what this could be.

You can create each item separately, and make each have no powers on its own. Then on one item have a check (Epr-req I think) that looks to see if all three items are equipped. If they are, grant the powers of the set. Or as Mathias suggests above for making a set and having it add the three items.
Size increase - Make sure you don't have an adjustment or another item on the Hero increasing size. Check the scripts on the items you have created - one must have something you didn't expect or intend doing this.
If in doubt, post your userfile here and we can check & offer advice.