Magento Datafeed Import

We have a new set of .flat files (.csv and tab) that I need to import on a regular basis (monthly at least) for potentially thousands of products. In an ideal world, I'd like to have a process and/or software to take the set of data files, convert them to a format that can be imported into Magento 1.5 using the new "Import" feature (custom app, web-based tool, Excel or Open Office are all OK solutions). Initial data file is for 5000 items with 32000 attributes total. Final project The data feed includes an item file, a master category file, and an attribute file (sample data files attached). Assume category structure exist in Magento database to match names of categories in data files (aka. import by category name). Attributes may or may not exist in Magento DB. Can be added as needed. Developer will have admin access to development Magento server for testing of import files. ftp/ssh access can be provided if needed as well.