Your /etc/X11/XF86Config-4 file probably needs some TLC. I'd back up the existing one, and give this
one a go. (Incidentally, www.linux-laptops.net
is usually the best place to go when you have troubles with laptops running linux). So, when you reach that white screen, press CTRL-ALT-F3 to switch to another console, login as root, and:
mv XF86Config-4 XF86Config-4.bak
cp /floppy/XF86Config-4 .
umount -l /floppy
This assumes that you've downloaded the config file onto a floppy, and renamed it to XF86Config-4. It also assumes that your floppy is mounted at /floppy, which may not be the case (I'm on my Debian system at the moment) - it might be /media/floppy or /mnt/floppy. Or you could put it onto a re-writable cd, and mount it via mount /cdrom, mount /media/cdrom etc.