How do I join the NXT 2.0 (Ardor) distribution if it isn't an ICO? And how does it affect NXT 1.0 holders? Can someone explain to me how to join the NXT 2.0 (Ardor) distribution? I've been reading you can't buy into the coin initially or can you? Also how does this affect NXT 1.0 system? It seems to be one of the first blockchain to implement a child-chain technology with Proof of Stake mining?
The Ardor launch will happen in 2017, but the distribution of the main ARDR tokens will be based on the Nxt 1.0 balances. And yes, as far as I know it is the first scalable blockchain platform using 100% proof of stake.

Starting the next 14th of July, the Nxt network will take a snapshot of all the account balances every hour. This will last for three months. At Nxt network block 1,000,000 (due for October 12th) every Nxt account will receive an amount of Ardor assets equal to the average of all the snapshots taken - so you'll get as many Ardor tokens as the average of your NXT balance during those three months. So anyone who holds NXT during the snapshots period, regardless of when the NXT were acquired, will participate in the initial Ardor distribution. 

After Nxt network block 1,000,000 your account still keeps the NXT you are holding at that block, as usual. And from that moment, ARDR assets also become tradable in the Nxt asset exchange.

When the Ardor network goes live next year, the tokens for the main Ardor chain will be distributed according to the number of ARDR assets held in each Nxt account at the moment of launch. This main chain and the ARDR tokens are the backbone securing the whole network, including all child chains transactions.

As for the Nxt 1.0 system, it will stay running and it will have its own roadmap aside from Ardor.

There's another aspect to keep in mind: as said, Ardor will have a main chain, fueled by the ARDR tokens, that secures all the transactions done in the whole Ardor platform, including all of the child chain transactions that may be created by platform users. The first among these child chains will be included at Ardor launch, and while the main ARDR chain will only include basic transaction types and the staking/forging operations, this first child chain will use a "transactional" token and include all the features currently working at Nxt 1.0, like the Asset Exchange, Voting or the Monetary System. 

The token for this first child chain (called "FNX" in development discussions so far) will also be distributed according to the existing Nxt 1.0 balances at the time of Ardor launch, and a percentage of this first child chain tokens will be held to fund the platform development. Initially a 50% of these first child chain tokens was proposed to sustain Ardor funding in the long run, but the percentage is still open and it might be smaller depending on how things unfold in this upcoming months.

So, as a tl:dr;

Nxt 1.0 users will receive at network block 1,000,000 an amount of Ardor tokens equal to the average NXT balance in their accounts from July 14th to block 1,000,000. The NXT will remain in Nxt 1.0 account balances, and then ARDR can be traded in the Nxt Asset Exchange.

At the moment of Ardor launch in 2017, every account will receive an amount of Ardor tokens equal to the number of ARDR assets it holds, and an amount of the first child chain tokens ("FNX") equal to the amount of NXT in their balance at that moment, multiplied by a % coefficient to be determined, but at this moment set at 0.5 (i.e. 0.5 "FNX" for every 1 NXT)