No, you can't get the CD key that way. That would be your wonid.
If that were the way to get the cd key, then everyone online would have acccess to everyone else's cd key, that would be anarchy.
CD key can be found in the registry by going here:
go to start -> run -> regedit
> in there go to the folder:
> My Computer\HKEY_CURRENT_USER\Software\Valve\Half-Life\Settings
> in the cdkey is stored in there. to change it simply double click "Key",
> which is toward to bottom.
If you look at both, you will see the difference.