Is it possible to set up a calendar in office 365 that is accessible to everyone in my office? I would like to set it up so that when one update is made, by any user, everyone can see it...
Depends on the exact requirements. If you want to actually be able to send meeting invitations from this calendar, you cannot use SharePoint calendar, you need Exchange one. What Frosty555 suggested will work, and if you need everyone in the company to be able to make appointments in the said calendar, simply edit the default permissions.
The cmdlet you will need to do this is: http://technet.microsoft.com/en-us/library/dd298062(v=exchg.150).aspx