You are completely missing the point of his question and since i have the same question let me try to explain the problem:

You have provided the customer with a quote for services, your company requires a 50% deposit to order materials and lock in a place on your schedule.  When you are dealing with residential customers they will usually just write you a check for the 50% and not ask for an invoice.  However when you are dealing with Condo Associations, Corporate Plazas, Country Clubs, Municipalities, or similar businesses they want you to provide an invoice for the 50% deposit.  Since Quickbooks (in our case Enterprise 22) does not have any deposit request templates or the like you have to create an Invoice. (This will of course infuriate your accounts since now you will need to pay sales taxes on services that have not actually been performed.)

So you say to your self, hmm  i could make a progress invoice.  Which is what it appears he was doing, so when you make the progress invoice it cuts the quantities in half.  I'm sure the folks at QB think this is what should happen, but oh no when you do that and are dealing with the common person this creates mayhem - almost every time no matter how many ways you explain it one of two things happens 1) the customer then thinks that they should send in a check for 50% of that amount so you end up with a deposit of 25%  or 2) the person pays the 50% deposit but then when you go to invoice them for remaining 50% they think you are trying to pull a fast one and double bill them and refuse to pay because the quantities shown on both invoices are the same.  Resulting in much wasted time on phone calls and e-mail trying to explain why the need to pay.

How could quickbooks solve this problem?  Very simply add a deposit request feature  - this would look like an invoice for the full amount with all quantities showing, with two major exceptions 1) after the Subtotal/Taxes/Total lines at the bottom a new line "Deposit Request for ___% = $          "    where you can tell QB what percent to calculate and it does the math.  2) this is does not get recorded as an invoice, its a new category similar to estimates. You would record the deposit when it arrives and after the work is completed the deposit is then applied to the invoice. 

Unless i have missed in in my 20+ years of using quickbooks there is not a way to currently do this.