You can't just open the clients from that site, you have to Diff them. http://rathena.org/wiki/Hexing
Also you didn't answer my question before, how did you download rAthena to begin with? Please don't tell me you saved each file one by one xD
Oh and to answer your question about the full / lite clients, a lite client is the exact same as the full, but doesn't have the Data.grf file or BGM folder generally.