The Beta's available for download right now, I've been using it for a few months at home and in a testing environment at work.

It's completely backwards compatible, from what I've seen. You have the option to save as an Office 2007 document (a .docx) or as a standard 2003 document (.doc). The translation seems pretty solid. I guess the one issue you'd run into is that you couldn't use 2003 to open a 2007 document saved in its native format. But then, you wouldn't be able to do that with WordPerfect either. Seriously, give the Beta a try. It's only like two bucks to download.

Not to sound like a shill for Microsoft or anything (I have serious, serious doubts about Vista), but they really have hit the ball out of the park with Office 2007. They've completely redone the user interface, making it much simpler and much more streamlined.

But even if you moved into another office suite, say Wordperfect or Lotus, I guess I'm confused as to why you just couldn't keep using your Outlook 2003 as your email client. Email is email, much more universal than wordprocessing or spreadsheets. The messages I POP or IMAP from my server to my local client are the same, regardless of whether they're going into Outlook 2007, 2003, Eudora, whatever.