Sorry, but i can do this work in open office spreadsheet and send it attached by email myself. Same amount of work and keep Joomla website simpler.
The *FREE* *LITE* edition of nBill does not pretend to be a complete billing system, nor even a basic one. It is a way of quickly producing professional looking invoices *and allowing people to pay them online*. If you produce your invoices using a spreadsheet, that does not allow the client to login to your website and see their paid and unpaid invoices nor to pay them online. It has nothing to do with Virtuemart. Just because it does not fit your particular requirements, that does not make it useless! It does exactly what it says on the JED.