Commodity Classification Structure
When setting up the structure, I believe the more important aspect is the Product Classification, not the actual "code". The code can be alpha or numeric or alpha/numeric depending on your requirement. The classification is where the attention should be focused, initially.
For example, if you want to classify your computer "stuff" on a very high level, you could classify: Communications & Computer Equipment, Hardware & Accessories, Computers, etc. Then once you have defined the high level classes, add more detail to each one, i.e., Computers (laptop, desktop, etc.). You can then really anal and break those down further (Dell, HP, etc.) Then, you can assign the "code" to each.
Try this approach, it may work well for you. Hope it helps.