There is a MSI package in each site at ~\UI\ActiveX\EPiServerOfficeAddin.msi
Read more about Installation of EPiServer components.
Can I please follow up on this - is this information accurate for CMS 6? A client asked me the same thing today.
Looks like it when I look here: C:\Program Files (x86)\EPiServer\CMS\6.1.379.0\Application\UI\CMS\ActiveX
I got a qustion from one of our customers today. Does it exist redistributable packages for client components and office addin that could be pushed out instead of the users installing it themselves which is a problem since they aren't administrators on their computers.