Applying invoices to prepayments

We are contract plant growers on Maui.  I receive growing deposits from customers.  I have never been able to figure out how to input the money received and then applying invoices against the amount over a 6 month period.  We can't figure out if in the Receipts window, we need to set up a new Cash Account or what.  We're just been doing this manually on an excel sheet but I know there must be a way to do it.

We once applied the running invoices to Items Sold but at the end, the "item sold" line on the balance sheet was off.

Please help us.  I am using Peachtree by Sage 2009.  I'm one of those old timers that cannot deal with too many upgrades so I had a 2000 version and 5 year ago, I upgraded to 2009.

Mahalo