I'm have this problems as well. I really need help and hope anyone can share your ideas or solutions.
My case is :
1.) Windows Xp with Outlook2003 or Outlook2007 connect to exchange server 2003 without any problems (outside and not in company network)
2.) Windows 7 Ultimate 64-bit with Outlook2003 or 2007 CANNOT connect to exchange server 2003 (outside and out of company network) but I can connect without any problems in company network.
3.) check with ISP and without any port blocked
4.) already edit hosts file in Win7 Ultimate.
Hope someone can help. Please......