"When I boot, after the splash screen, I get the error
Invalid or unsupported executable format.
Filesystem is ext2fs, partition type 0x83
kernel /vmlinuz-2.4.20-8 ro root=/dev/hda4"
This is probably a problem with grub. Look at /etc/grub.conf and see if there are any problems. In particular check to make sure that you have the right file system type for /. After you are sure that /etc/grub.conf is correct you may need to run grub-install.
here is a grub HOWTO:
Be prepared. Create a LifeBoat CD.