One of the most notable additions to Microsoft's 2007 Office System was the Trust Center, which centralizes the security options in Word, Excel, Outlook, PowerPoint, and the other applications in the suite. Of course, this being Office, it figures that many of the most important security features--including the new Document Inspector--also reside elsewhere.
To open the Trust Center in the 2007 versions of Word, Excel, PowerPoint, and Access, click the Office button, select the Options button at the bottom-right of the window, choose Trust Center in the left pane, and click the Trust Center Settings button in the right pane. In Outlook 2007 and Publisher 2007, click Tools > Trust Center.
The security options presented in the Trust Center vary from program to program, but you'll likely want to start by clicking the Privacy Options button. The third and fifth options under Privacy Settings in the right window are checked by default: Download a file periodically that helps determine system problems; and Check Microsoft Office documents that are from or link to suspicious Web sites (this last option is missing in Outlook 2007).