Basic accounts payable application ?

I need to add an accounts payable module to my company's forms application which goes as far as producing customer invoices.

As a novice, I'm struggling a bit and thought that there must be thousands of forms out there doing just what I want - calling up a client account by name or numeric id, seeing what invoices are outstanding, entering a payment and allocating it against various invoices.

Can anyone e-mail me a form that I could check out and give me pointers to developing my own ?

Thanks in advance.

-- 
Mark