You can't use the files used by other LoL servers like NA / EUW / AUS to play in garena server. You have to download their own client. But if you could find the garena LoL installation from a friend, you can just update it and play.
Thanks for the info Nalti, +1
hey anyone from EUW ? i am DarkReaper999 from EUW, add me cz i havent seen any SL players in my server, if u like add me for a fun match, bored without a team :S