Google spreadsheets might be what you want to
have many users updating as a group project.
As a spreadsheet it's not that good but for your
type of use it might work better for you.
http://www.google.com/intl/en/options/
Of course you've not given any idea of how many
people, the size of the worksheet. If you have
privacy concerns then this would not be a viable
solution.
My own brief encounter with Excel shared workbooks
can be summarized as how to unshare the workbook
without having to restore from a backup.
Tools --> Share Workbook --> uncheck option
Highlight, Change Highlighting
http://www.mvps.org/dmcritchie/excel/highlite.htm