MS Technet blog post on Server 2003 SP2 breaking things on ISA 2004

"After installing Windows 2003 Service Pack 2 on SBS 2003 with ISA 2004 installed, you may experience the following problems:
-You can no longer successfully connect inbound using VPN (Clients get "Error 800: Unable to establish connection").

-You cannot reliably connect to the Internet using SecureNat.

-Some Outlook clients will fail to connect to the Exchange server (even with ISA 2004 SP2 and KB930414 installed)."