When i installed the game, I had a serious problem with my graphic card (Ati Radeon Mobility X300). I was running with the default drivers (non proprietary drivers) for the distribution Ubuntu Dapper Dake 6.06. My game just crashed and  my hole system freezed. It seems the problem is related with the non propritary drivers. I fixed the problem by installing the Propritary drivers supplied by ati. The installation procedure is described here : http://wiki.cchtml.com/index.php/Ubuntu_Installation_Guide#Method_1:_Installing_Dapper.27s_Included_Driver_.288.23.7.29

I posted it in case someone has a similar issue.