You can buy Level 2 of Harvesting without registering the game. I have played the game unregistered for more than a day (more than once) and had a very healthy tribe the whole time and was able to train many of them very well.

Purchasing and registering the game allows you to attain all of the tech levels, solve all of the puzzles, and grow your population to much higher levels. The unregistered mode is designed to give you a feel for game play. If you still have more specific questions, feel free to send me a private message!