System Requirements

Outlook 2007, like the rest of the Office 2007 suite, requires Windows XP Service Pack 2 or newer for the client operating system, with at least 256MB of RAM and at least 2GB of hard drive space. In reality, of course, running Windows XP, much less Office 2007, in 256MB of RAM is not a very satisfying way to work, so we recommend a bare minimum of 512MB of RAM; really, you should aim for 1GB or more if you can. Especially if you're running Vista you'll want the 1GB of RAM, and to get the benefits of Vista's Aero interface, you'll want a video card with at least 128MB of memory on board.

Since you're reading a book about Exchange 2007, it probably isn't necessary to mention that Outlook 2007 is not supported by Exchange versions prior to Exchange 2000. It's time to finally migrate off those old Exchange 5.5 servers if you still have any in use.