he has an external HARD drive not a CD drive...
Buy or borrow a USB OPTICAL drive
OR install the destination drive for the OS into another computer that has a working optical drive
and run the installer, at the second reboot during the install disconnect the power before the computer restarts and move the HDD into the intended computer and let it boot.
This SOMETIMES works with XP, but I've never tried it with Vista or 7
Failing that borrow and install (alteast temporarily) the optical drive from another notebook computer...
There are typically some "appliances" screwed to the outside to make it fit the specific
notebook computer chassis, but with a bit of patience you'll figuire it out.