If you made image from his vista it should be bootable. If you copied only files from dvd to hard disk, use vlite. Open vlite, select folder where vista files are, then in options selec Make bootable DVD and it will create bootable dvd.
I aiways use "vLite" => can make bootable dvd - copy your vista to drive c:>vistadvd - open vlite => browse to vistadvd - look the menu box you will see "Create bootable iso" - done!