[lubuntu] 13.10 best video driver on iMac 17 PPC

Hi folks!

I'm a total newbbie, and I've installed correctly lubuntu 13.10 alternate (install_powerpc64) on my old Apple iMac PPC 17 here the full specs:
http://www.everymac.com/systems/appl...g5_1.6_17.html

very often the mouse arrow vanish and I can see a mobile part of the screen like a CGA video... I think it's a problem of video driver...

can anyone guide me to update / use the best video driver I can use / install easyly? (if possible via PPA ... )

thanks you in advance and sorry for my stupid question