If your firm is small than manual operations maybe details in spreadsheet would work but in case you have tonnes of inventory than would suggest to go to an automated software which is as per your requirement.
Classify your inventory into different types which shall make the work easier. You may take help from your accounts team for classification. for example IT Inventory, Non-IT Inventory and so on.
If required you can tag your inventory.
19th April 2013 From India , Mumbai