Hey Noel, that file will install the Lite client, which is what is showing in Add/Remove. So I'm not sure what your goal is. If the goal is to install the full client then use EVClientm.msi, where is a number indicating the User Extensions version.
Now, if your goal is to see the EV buttons then it's possible that your mailbox isn't successfully archive-enabled. Does this same issue exist with other mailboxes as well? How about other computers.
Check this cut and paste out:
User Extensions
The User Extensions provide the maximum functionality. In addition to the basic functionality of archive, view, and restore, users can view the Enterprise Vault properties of mailbox folders. If you allow them to do so, they can also modify these Enterprise Vault properties.
The User Extensions are supplied as a Microsoft� Windows� Installer (MSI) kit, which contains EVClientm.msi, where is a number indicating the User Extensions version. You can deploy the MSI package using an Active Directory Group Policy as described in Publishing in Active Directory.
Lee Allison
http://enterprisevault.typepad.com/the_ev_blog/