I found Urwigo to be the best. The Groundspeak one is terrible. And Earwigo is a bit cumbersome and you need to register with the owner of the site before you use it. It is actually web based. You don't have to download the software. Petr (Marcipanek) went to a Cache Event in Prague, Czech Republic last fall that was actually an 8 hour class by the writer of the Urwigo program, on how to build Whereigo cartridges.

Cano, I don't think your Whereigo challenge will meet the current Challenge Cache guidelines. I dont think you can create a Challenge that requires someone to place a cache ha ha