2 Q's. Invoice Statements

Hello, I'm hoping that somebody can help me out. I have spent the last 2 days trawling through this resource and others looking for the answer with no result.

I have produced a fm system for my my graphic design business. Its fantastic (the software that is, not necessarily my system) and has eased up the workload considerbly. However there is one area that needs attention, namely sales invoice statements.

Basically I want to produce sales invoice statements for my clients that display the total of: 'Invoices that are Over 30 days due, Over 60 days due, Over 120 days due.

The invoices at the moment capture the 'Total' and 'Issue Date'. I think that I should be able to produce 3 calculation fields that will work out which files have a greater difference between the Currentdate and the date off issue of 30 (60, 120 etc), then get a summary of the running total (I have a summary field set up capturing the running total of the invoice total. I have tried but so far nothing is working, any ideas?

The other problem was that at the moment I perform a find for all Unpaid invoices, then I have to record (with a pen and paper, sorry) the clients and then perform another find for the client name and status = unpaid. I would love to be able to run a script that found all unpaid invoices, then grouped by the client name and printed out a statement list (showing the 3 fields above of course).

Hopefully somebody can help me out,

Cheers

Johnny