Linking two separate companies

The company I work for has joined forces with another company to manufacture and drop ship many of our products for us. Basically, we will handle all sales and some light manufacturing, and they will handle the more heavy manufacturing and ship and bill our customers directly, giving us a commission for the sales.

We of course still need to track these sales and keep track of order status on our end. The problem is they have their own accounting program (Kewill), and we have ours (Business Works). We have information in our system we do not want to necessarily share with them, and vice versa.

Currently, we are doing a lot of duplicate entry. We receive and enter an order, fax it to them, then they invoice, fax it to us, and then we generate an invoice for our system.

We need to find a way to intergrate our systems somehow. We would also like to offer electronic order for some of our larger customers that are already set up for that sort of thing to further simplify everything. I am looking for cost-effective suggestions. Can someone please offer me some advice on how this may be done? I've been looking into edi, a new accounting system entirely, online applications, etc. but am getting into areas I have no experience with. PLEASE, any advice??