Does anyone have a macro'd spreadsheet for seller financing?

[Nathan Hall]

I'd like to be able to put in amortization schedule (term), rate, down payment, monthly payment adjusted to a fixed point, and get proper accruals of principal and interest by month and year. With the option of "if we pay it off at any point, here's how much you get limo sum."

Apologies if this is a basic request but I'm absolutely terrible with spreadsheet macros in general.