If the "prepare piece" message is stuck, it usually means the site is still generating the download link or the archive is split into multiple parts (Part 1, Part 2, etc.). Make sure you have or 7-Zip installed.
Since this specific version is quite old (the game has since reached its full 1.0 release), here is the best way to handle this file: 1. Arquivo: Empires.of.the.Undergrowth.v0.30111.zi...
If you enjoy the game, I'd recommend checking out the on Steam or GOG. It includes the full campaign, many more ant species, and much better optimization than the older v0.3 versions. If the "prepare piece" message is stuck, it