So you got yourself a DirecTv box that is capable of supporting DirecTv2PC. You have installed the soft, got your activation code, but unfortunately are not able to activate the DirecTv2PC on your computer due to inability of the program to connect to the web. You were careful enough to unlock the 443 port on you router and enable it in your firewall settings, but it still won't work.
Here what you do to resolve the issue:
Locate hosts file, usually in C:\WINDOWS\system32\drivers\etc.
Insert this text: 188.8.131.52 activation.cyberlink.com
Save, without changing an extension of the file.
That's it. This works beautifully on WinXP SP3.
Edit Oct 23, 2008: For the info on how to change the content of the hosts file on Vista, please follow this link to the Tim Hibbard post.