PHP MySQL and SAGE Line 50 Importer

I want to create the ability for my users to simply download invoices and expenses into excel and then import them into SAGE. I will need to import sales invoice and accounts receivables payment, expenses and expenses payment. I have four seperate tables.? I have no experience with SAGE (but am a PHP developer)? so may need guidance with what fields etc SAGE require. EDIT: AFTER LOOKING ONLINE FOR SIMILAR PROJECTS, I REALISED THAT THIS MAY NOT BE POSSIBLE USING THE SAGE INTERFACE.? IF IT ISN'T POSSIBLE THEN I UNDERSTAND A SMALL .NET APPLICATION MAYBE REQUIRED.