Installed latest distrib to Windows XP machine on an external HD. Followed all defaults, perfectly smooth install. Rebooted machine, no GRUB, no choice, went right to XP. Was GRUB installed only to external HD? Do I have to install GRUB to c:\ drive? How? Thanks
There is no C:\ drive in Linux, only Windows. If you installed grub to the USB drive's MBR, you need to go into BIOS and set the USB drive as the boot drive. If you installed grub to the / partition of the Linux installation, it will not boot at all without another bootloader (grub) installed to the MBR.
If your computer is incapable of booting to USB because of BIOS restrictions, You would need grub installed to the MBR of the internal hard drive, linked to a copy of the Linux /boot directory somewhere on the internal drive, with the boot stanza of /boot/grub/menu.lst modified to boot the kernel from the internal drive, but use the USB / partition.
To do the latter, you need to first copy the entire /boot directory to the internal drive, usually on a small Linux partition created on the internal hard drive for that purpose alone. 50 MB would be more than sufficient. Then a grub native install to the internal hard drives MBR. If a Windows stanza is not automatically created, one can be easily added manually.