Excel 2007 : Linking workbooks

I have created a form which is for the sales department to fill in for each new customer. I have protected the worksheet so they can not change it. The cells that I want to track the information on is linked to another worksheet with the column headings required.

The problem that I can not solve is how each sales rep can save the source document by changing the name and still have it update the linked cells to the sheet by adding the linked information to the next set of empty cells available. The documents will all be in the same folder but not the same workbook. I am using Excel 2007.

Is this even possible? I have experimented and found out that it will update the summary sheet but it replaces the information, I need it to fill in below as the documents are saved separately under different names than that of the original document. Please help!