knoppix now displays using the whole screen, but even after reinstalling ubuntu it still just displays in a small area in the middle.
Any ideas on how to fix it? (apart from installing gentoo)
Well, the quick-and-easy way (relatively) would be to boot up Knoppix again, and then look at the X config file it creates (it will be at /etc/X11/XF86Config-4
). The important bits will be towards the bottom -- in the Display section, look for the driver (it might be 'radeon' or 'vesa'), and also the Screen resolution section below that. Now just edit your /etc/X11/Xorg.conf file so that it uses the same resolutions and screen drivers.
Note that you can actually edit your Ubuntu Xorg while running Knoppix -- just open up the file (after mounting the hard drive read/write -- the default is read only).