Kernel parameters for Macintosh Powerbook 3500/G3 ("Kanga")

I am trying to get Xubuntu 6 installed on my old Powerbook. The problem seems to be the video mode. The installer starts but the screen output is addressed only to the upper half of the monitor and is additionally garbeled although one can still guess what's going on. According to a list on the internet the kernel parameters one should pass using BootX it should read:
video=chipsfb:vmode:10,cmode:16 However, there was no difference when using these parameters. Funnily an older version of Ubuntu addressed the monitor correctly but failed upon the first boot after installation to do so.