Thank you for the information. Even I was not quite sure if this system for partial payment was possible or not. Good to know that upfront and down payments are possible with the help of the partial payment extension.
The main issue I can see with doing partial payments is to do with taking the second part of the payment. To have it so it automatically takes teh second part of the payment would require the use of a payment processor that supports follow up transactions and any module to handle this would I imagine need tto be firmly integrated with teh payment gateway in use. The FME extensions module linked to above seems to get around this by having the customer initiate the follow up payment (at least that’s how I read the extension description). This obviously gives the security needed and lets the customer choose payment dates etc but I’m not sure if this would suit all scenarios.
Using tokenised cards such as Cybersource offer could be used to achieve this or a payment gateway that allows follow up transactions that can be linked to an existing transaction could be workable but as I sais earlier this would need to be heavily integrated into the payment module itself from what I can see.