OK, I should really finish the documentation, it will cover the inventory definition (among the other things).
But I will give you a brief description now. Open the WME demo project in ProjectMan and open the "interface" folder. There is a "inventory.def" file, which defines the layout of the inventory box. As you can see, you can define a space reserved for each item (ITEM_WIDTH, ITEM_HEIGHT). Now, the important thing is the "AREA" line. It defines a rectangle on screen, which will contain the items.
The definition is as follows:
AREA { left, top, right, bottom }
For example, if you want the area to cover the whole screen, use
AREA { 0, 0, 800, 600 }
The engine will automatically fill this area with items, and if the items won't fit, the "next" and "prev" buttons will be enabled.
Once again, I will describe this in the documentation in more depth.
