Invoices and Quotes Set up - Exc GST with sub total and GST as a line item

Hi,

I am trying to alter our quotation and invoice settings for the line items to be exclusive of GST, then have a subtital and GST added as line item followed by an overall total.

I have tried changing the layout and settings but have been unable to locate a specific cutsomise tab.

Any ideas on how to fix this would be greatly apprecaited :-)

Thanks