Hi, Dissolution!

All 1.0 players (whether you have legacy status or not) get a free download of A Realm Reborn. You already bought it once, you don't need to buy it again.

If you have access to the beta forums, you can now download the launcher here. This will be used for both the open beta client and launch.

As for not being able to register your copy of 1.0... I'm a little confused? Are you trying to register a second copy of the game to your account? Your registration code you used when you first started the game is all you need.