new hdd

I have just purchased a second used pc.It had a bad hdd so purchased a new 500gb segate.
my question is:
with no way to boot the used hdd how do I install the new one ? I have a windows 7 iso to install on the hdd.you can't use a hdd from another machine so how do I boot the used machine.
Thanks for any help/info

Burn the ISO to DVD disc.

Have a look at those tutorials:
http://www.sevenforums.com/tutorials/91339-ssd-hdd-optimize-windows-reinstallation.html
http://www.sevenforums.com/tutorials/1649-clean-install-windows-7-a.html?ltr=C