Pinnacle cart / inventory update script

Our eCommerce store is hosted on the Pinnclecart shopping cart platform. Our inventory needs to be the same as our supplier (dropshipper). They send us daily inventory updates via Excel spread sheet. Manually updating is getting time consuming and we are considering a script that could automate the process. Note: There is a built in feature within our Pinnaclecart to download a CSV file of the inventory and then upload the edited file back. So if there is a possibility to build a script that will compare 2 Excel spread sheets and update the CSV one so it can be uploaded back to the site, that could work as well. The script should also either add new items or produce a list of items that are not listed on our site. Please ask any questions you may have or if you need to see a copy of either of the Excel files, etc...