If you want a more full-feature WarCraft Clone, you can check out n0p’s Wargus port. It uses the Strategus game engine and WarCraft II graphics to make a WarCraft-like experience on the PocketPC. But it requires a huge amount of memory. You also need to have a copy of WarCraft II in order to play, and the setup process is rather complicated.
Medieval, on the other hand, is less than 1MB at present. All you need to do to play is unzip the file and copy it to your PDA. Now if someone would just create a StarCraft port, and not get sued into oblivion in the process.