C# app to compare two excel files

A C# application to run on Windows XP or Vista to compare 2 MS excel files or csv files and generate a report showing discrepancies between the files. The user should be able to select the two files stored on the system that the app is running on and then save the resulting report as an excel file with a name of their choice. Each source excel or csv file will have a column with the header 'sku' and a column with the header 'qty'. The sku is the unique identifier, and the discrepancies should be in the qty column, however both files may not have all the same sku numbers. The resulting report should differentiate between three types of discrepancies. Type 1 is when the sku is present in both files but the qty is different. Type 2 is when the sku is present in the first file but not the second. Type 3 is when the sku is present in the second file but not the first. The final report will display this with three columns: 'sku','qty_1','qty_2'. The qty_1 and qty_2 columns will be populated with the value 'N/A' when the sku was not present in either the first or second source file, respectively.