Share Excel file in Compatibility mode
 

I have an Excel '07 file that I created for shared use; however, the users
all have '03. I'd like to keep it in '07 due to size. I had them download
MicroSoft Compatibility package in order to do this; but, when they only open
this Excel '07 file in compatibility mode, it only allows them to be in "Read
Only". Is there a work around solution so that I can keep this file in '07
and they can use it as a share file without upgrading them?