There is an interesting posting on the MS Exchange team blog (http://msexchangeteam.com/archive/2007/02/07/434523.aspx) regarding OWA in Exchange 2007 and coexistence with Exchange 2003 and 2000.

Some things that stood out for me:

• "OWA 2007 also doesn't support Exchange 2007 public folders yet. Look for it in an Exchange 2007 Service Pack" (emphasis mine)
• "You should replace all your E2003/2000 FE servers with E2007 CAS servers before moving your mailboxes to E2007" (already known, but bears calling out again)
• "Note that a CAS will require more powerful hardware than an FE server, so account for that in your planning (see this blog post for details)" (again, bears calling out separately)
• Great explanation of how authentication is handled, so users get prompted for credentials the minimum number of times (just once, in most cases).
• Great examples illustrating various coexistence scenarios, leveraging exprox and davex.

And, explaining how to access public folders through E2007 OWA, until the promised functionality is delivered an a service pack (again good to call out).

Andy