small business

I have a small business and we have a neighboring business that works with us but has not developed a spreadsheet / database to do business through us. I need to setup an integrated spreadsheet into a webpage that will post the data to a file on our server which we can access and keep records of. This is mainly just for invoicing since we deal with selling citrus (they grow it, we buy it). What would I have to do in order to set up a form/spreadsheet integrated into a page that could be logged into and have the data entered transferred to either a finalized spreadsheet or atleast to an invoiced version of it.

In short I need to allow them to login and enter the weight, cost per lbs, and PO number of anything we order from them and have it calculate the cost like a regular spreadsheet and have it post to a file on our server.

Hope this makes sense and somebody can point me in the right direction. I think that I just need to find an integrated spreadsheet script/program and set up the formatting but I am not sure how to have it post to our server or how to lock the page for them to log into before using.

Hire a programmer. This will not be an expensive job, you can post on sites like http://www.odesk.com (I have no affiliation with them) and people will bid on the job. I urge you to not try this yourself, it sounds like you don't have any idea how to accomplish this task. Make sure to get all your requirements clear if you decide to post a job.