USB Utility Disk
These are approximate instructions for putting Memtest86 and Hitachi Drive Fitness Test on a USB Flash drive (written mostly from memory).
Install GRUB on a flash drive
Find the device name of you USB flash drive, mount it, and install grub to it.
mount /dev/sdb1 /media/usbdisk/
/sbin/grub-install --root-directory=/media/usbdisk/ /dev/sdb
Download memtest86
Download the memtest ISO image from www.memtest86.com
Downloaded FreeDOS distro
From the FreeDOS site, download a FreeDOS distribution like this one fdbootcd.iso
Downloaded Hitachi disk checker
You can get a free Drive Fitness Test program from Hitachi. I used the binary disk image.
Mount image
Mount the FreeDOS ISO and Memtest86 ISO and move images to USB device (assuming mounted on /metdia/usbdisk).
mount fdbootcd.iso /mnt/cdrom/ -o loop
cp /mnt/cdrom/data/memdisk /media/usbdisk/memdisk
cp dft32_v406_b00_install.img /media/usbdisk/dft.img
umount /mnt/cdrom
mount memtest86-3.2.iso /mnt/cdrom/ -o loop
cp /mnt/cdrom/boot/memtest.img /media/usbdisk/memtest.img
Modified grub.conf
Add the following to your /media/usbdisk/boot/grub.conf on your USB device
title Memtest86
kernel /boot/memtest.img
title Hard Disk Checker
root (hd0,0)
kernel /memdisk floppy=0
initrd /dft.img
Boot it and test