Eh the thing is that it's still not finished; so anything that I give you would be a pile of crap because you would have to practically re-write it to fit your system. Typically an inventory system has tie-ins to stat systems and quest systems, etc. I can give it to you in a nut shell:

Use a panel for the inventory screen, use windows on the panel to display a section of an image file (all icons placed on a single "sprite sheet"), place a button over each window on the panel with an invisible image the size of the window object, each button controls a specific slot. When clicking on a button, the data from one section of the array is copied to another, I generally use position 0 on the array to indicate the cursor.

I've done lots of inventory systems in the past, I have just never shared them with anyone because I noticed that mine were totally different from the way others were doing it. This one just uses some of the cool new lite-c functions that make stuff neater. Like I used to use a different panel that follows the mouse to display an item "in" the cursor; now I use the bitmap cut out thingie, which just draws an icon under the cursor.

The only way that this inventory system differs is that the panels, buttons, and windows are all created during gameplay, and not pre-defined.