VM Pre-order installs with one click and no code modification and works great "right out of the box". You can set different deposit amounts for each product either as a fixed fee or as a percentage. The customer then has the ability to pay just the deposit or the entire amount if they prefer. If they pay the deposit, their order status is changed to "Partial" so it is easy to track who still owes.
Jeremy, the developer is WONDERFUL also. He lists his phone number on his website and has answered the phone just about every time I have called. When he doesn't answer, he always calls back in less than 30 minutes.
When I first started using VM Pre-order, I needed it to do things just a little differently. I called him and explained what I needed and he got right on it wiht the changes ready that same day! I gave him superadmin access and he even went in and installed it for me. The next day, he had that update on his site for the rest of his customers to use. THIS GUY IS DEDICATED to his work!
I would HIGHLY recommend VM Pre-order for anyone who is running a VM site that sells items that frequently are out of stock. It will increase your sales tremendously!