Need to help "cannot install FTDIUBSSerialDri

Dear All, I'm using Mac OS X version 10.4.11. I downloaded Arduino software, but I couldn't install the driver. The computer showed "YOU CANNOT CONTINUE, THERE IS NOTHING TO INSTALL" when I installing it. I also didn't get the right Serial Port as Arduino web-page displayed. Please help me to solve this problem.

Tobby :(