Partial prepayment for purchase order

Hi,

Is there a way to do a partial prepayment for a unreceived purchase order?  For example I create a PO for 1 truck to be delivered in 3 months.  I pay a deposit of 10% upfront, 20% next month and balance when I receive the truck on the 3rd month.  I looked at voucher logging but I believe that only works for a full prepayment.  Prepayment voucher entry I believe only works for a standard voucher entry, unless I am reading wrong.

thanks

Kevin