At the current time, you can not trade with a capital of less than about $2000-$5000, dependent on your strategy script. This is not a restriction of Zorro, it is a requirement of the broker who demands a minimum margin of about $100 per trade. Due to the return fluctuations you'll then need several 1000 $ for trading safely. You can read details about that in the Zorro documentation.

Future Zorro versions will support special accounts with micro-lots. Then you can indeed trade with a few 100 $. This is intended for families in poor countries that can not afford a normal broker account.

With the beta version you better don't trade anyway - so this is only a theoretical restriction at the moment.