Here's how you can join the Free Play event on the PC/Mac:
•If you participated in any ESO beta or free trial, you simply need to log into your account and click the Try Free Trial button on the right side of the page.
•If you have never played ESO, click this link to create a new ESO account which will be activated for the Free Play event automatically. You'll be provided a download link once you create your account.
So, a friend has tried this and only gets "Redeem Code" and "Buy Now" on the right side. Where's the "Play Free" link? =D