By default, Outlook 2007 has contact linking disabled. In previous versions, it was enabled by default giving you a field on most forms that you could use to link a contact to an item which would then show up on the Activities tab.
To enable Contact Linking:
1. Click Tools and select Options.
2. Click the Contacts Options button.
3. Check the Show Contact Linking on all Forms checkbox.
4. Click OK to close the Contact Options dialog box.
5. Click OK to close the Options dialog box.