As you can make visual reports with MS Project 2007 and anyhow can add Custom fields, I am still wondering what you want to achieve in Excel that would not be possible in MS Project.
There are sometimes text changes I will do in Excel, just because it is easier there to do text manipulation. However, in general, MS Project is THE product to do anything about scheduling.
Therefore I am very curious to know what you would do in Excel that is not possible in MS Project, apart from some report charts. That possibility is now incorporated in MS Project 2007 and above.
Up to now, only the text manipulation and some pre-calculations before entering data into MS Project, have been for me the only needs to use Excel as well.
There might be a potential other use. If people don't have MS Project, an export to Excel might perhaps be useful. However, normally I would make a pdf-file.
Theoretically one could export to Excel, change some data and merge these again with the plan in MS Project. If remote amendment [such as Actual Work] would become a frequent goal, there was in the past an easy Outlook tool. Today MS makes is necessary to use the expensive and complicated MS Project Server. If you would have many project with shared resources on several locations with a need to constantly updating your projects, then MS Project Server may become essential.
For simpler combinations of projects a resource pool may do. I get the feeling, perhaps wrongly, that you have just a rather simple project, being more used to Excel working with that where probably MS Project itself could help you as well. This is not uncommon, as most people believe that they can just start using MS Project and real good (advanced) MS Project courses are more or less rare.
I am still awaiting both files and a more detailed explanation what you want to achieve. Maybe I can be of any help although miracles are not always readily possible. Others could also contribute with good solutions as there is hardly ever a single solution for a given problem. A lot remains a matter of appreciation. That could also apply to your wish to use Excel.
Why an easy solution if you can make it complicated?
Greetings from the Netherlands