Instead of using one big file, You should use a database. Yes, You can store various types of files like gifs in the database if You like to.
The file would not be human readable or accessible by non-technical users, but this is good.
The database would have a website that Your non-technical users would use to insert, update and get data from. They would be able to display it on the page or export it to csv (or even xls - it's not that hard, I've seen some csv->xls converters). You could look into some open standard document formats, I think it should be quite easy to output data with in it. Do not try to output in "doc" format (but You could try "docx"). You should be able to easily teach the users how to export their data to a CSV and upload it to the site, or they could use the web interface to insert the data if they like to.
If You will allow Your users to mess with the raw data, they will break it (i have tried that, You have no idea how those guys could do that). The only way to prevent it is to make a web form that only allows them to perform certain actions that You exactly know how that they should suppose to perform.
The database + web page solution is the good one. Using VB or pywin32 to script MSOffice will get You in so much trouble I cannot even imagine.
You could use gnuplot or some other graphics library to draw (pretty straightforward to implement, it does all the hard work for You).
I am afraid that the "quick" and dirty solution is tempting, but I only can say one thing: it will not be quick. In a few weeks You will find that hacking around with MSOffice scripting is messy, buggy and unreliable and the non-technical guys will hate it and say that in other companies they used to have a simple web panel that did that. Then You will find that You will not be able to ask about the scripting because everyone uses the web interfaces nowadays, as they are quite easy to implement and maintain.
This is not a small project, it's a medium sized one, You need to remember this while writing it. It will take some time to do it and test it and You will have to add new features as the non-technical guys will start using it. I knew some passionate php teenagers who would be able to write this panel in a week, but as I understand You have some better resources so I hope You will come with a really reliable, modular, extensible solution with good usability and happy users.
Good luck!