to be honest Daniel H I think a database, rather than a spreadsheet is what you need.
If you've got Excel do you have Access?
Do you realise what you are taking on - you will have to allocate an unique code to everything in your inventory and a description/name - as a minimum.
You then have to have a system that monitors the inventory - goods in, goods out, lead times, minimum stock levels, etc - it's not just the software design, here, it's the physical systems you need to maintain the system as well - the stores requisition needs to get from the stores to the data guys for it all to work.
- unless you network the stores, of course - how far can you go?