yes, it should work then, but again the xp pc that you burn from, if it is , for example, a hewlett packard, then the boot.img will not work on a dell.
I say it would be easier to extract the img from the xp install cd, save to your desktop and then use imgburn to create a bootable iso from the hirens download and the .img file you saved to your desktop,
Try your way first and if it does not boot, then you can try the second way. Time consuming I know, but this way at least you will be able to boot to hirens, when you get this to work.