If your tracking functionality is either disabled (grayed out) or if Outlook prompts you to say that you have insufficient permissions to track an e-mail, it probably is because the role of the user for which you have logged into the system with, does not have the appropriate permissions.
In order to allow the tracking of e-mails, the user needs to be able to:
1) Create a new activity (Since tracking an E-mail essentially means creating an activity in MS CRM 3.0)
2) Read and Append to queues (For the CRM E-mail Router to read the original e-mail from the CRM mailbox)
Hence, the role that needs tracking permissions shall have the following checked:
1) Create permissions for Activities
2) Read and Append to permissions for Queues