Applications :: Merge / Consolidate Excel Workbooks?

I handle a bit of finances at a small business. Each week I pull out a report from a web-based economy system. That then opens in Excel. What I'd like to do is simple:

1. The first week I pull the report and mark some stuff on the Excel page (for example highlighting certain debitors, making comments, color fills etc.)
2. The following week I pull the report again, and now I'd like to merge the two together. That is, keep the data from week 1 (or replace parts of it, if that's relevant) and simply add the data from week 2 onto that same sheet, so all information is right there.

I thought that would be a no-brainer. Now I've tried to merge workbooks, consolidate data, looked at tutorials on youtube, read forum posts - the lot, and I still can't get it to work. (Brain possibly smaller than I thought).