Hi Richard
First of all, all you need to do is when a client has paid, is go into their invoice and change the terms to 'Paid' There is even a Paid Date too if you want to enter this. This marks up the invoice accordingly.
Then all you need to do to view which ones are due/outstanding, paid etc etc, is to click the 'Invoices' button in the main front screen. Then in the 'Terms column' click the actual word 'Terms' at the top and it will sort the invoice list in order of Paid, then the other terms you have set, then which are due. Click it again and it will sort again the other way round so that the due invoices are at the top of the list. Its this simplicity which makes keeping track quite easy.
Also remember, you can also view your graphical reports (amongst other things) to show figures for 'Paid only invoices' if you wish.
I hope this has helped.
Thanks
Kev
p.s. please feel free to contact me for any other queries.