Unpacking items requires a sandbox or proper rights. First you rez the item, then you open it, copy it to your inventory (root folder), and finally you clean up the mess on the land (if its done - leaving a mess). Optionally you move the box and unpacked folder to the appropriate place in your personal inventory.
This process is not very intuitive and unnecessarily time consuming (especially for noobs).
I would suggest making it possible to rightclick a box in inventory and unpack it directly to the inventory where the box is located. The same familar way how you handle zip folders on your desktop.
Best regards.