You will need to know which version of Microsoft Outlook you are running to determine which version of Ebsta for Bullhorn you need to install.
To find out which version of Word you are running, please refer to this article by Microsoft:
Outlook 2007
Outlook 2007 runs 32-bit so you will need to use this install link: http://install.ebsta.com/outlook/x86/OutlookEbsta.msi.
Outlook 2010
You will have either 32-bit or 64-bit.
If you have Outlook 2010 32-bit, use this install link:
http://install.ebsta.com/outlook/x86/OutlookEbsta.msi.
If you have Outlook 2010 64-bit, use this install link:
http://install.ebsta.com/outlook/x64/OutlookEbsta.msi.
Outlook 2013
You will have either 32-bit or 64-bit.
If you have Outlook 2013 32-bit, use this install link:
http://install.ebsta.com/outlook/x86/OutlookEbsta.msi.
If you have Outlook 2013 64-bit, use this install link:
http://install.ebsta.com/outlook/x64/OutlookEbsta.msi.