If you already added your CD-Keys to a battle.net account those keys will be tied to that account, and you will need log back on to that account to get the option to download the game's installation files.
The option to download the game should be available here:
https://eu.battle.net/account/management/download/?show=classic provided you are logged on to the account where you initially added the CD-Keys.
And just adding to the above, there is a more recent guide on how to download and install Diablo 2 with fixed images and updated links:
How To Install & Play Diablo 2 Without Discs/cd