I am also having the same issue except my error is:
Booting "Gentoo Linux 2.6.24-r8'
root (hd0,0)
Filesystem type is ext2fs, partition type 0x83
kernel /boot/kernel-2.6.24-gentoo-r8 root=/dev/hda3
Error 15: File not found
Press any key to continue...
I also have the white lines. I cant really read through them. Can anyone tell me how to edit my display settings in grub to get rid of the white lines? I am very new to Gentoo so please be gentle.