Once you have the ISO image you have to either make a Windows 7 installation DVD from it or make a bootable USB Stick. The link on how to make a bootable stick is given in a message from EzioAuditore. You may follow that if you prefer to make a bootable pen drive.
I prefer a bootable DVD because my computer is old and the BIOS don't support booting from a USB Drive. The method to do so is at
http://www.sevenforums.com/tutorials/548-burn-disc-image-iso-img-file.html. However you can do this intuitively with most burning software.
Once you are armed with one of them (bootable DVD or Pen Drive), then and then alone you shall be able to boot into the Windows environment. If you have never made a bootable disk/USB just take the image to a computer savvy friend with a blank DVD and he shall do it for you easily in a few minutes.
The burning speed should not exceed 4 as higher speeds might create a defective disk. But before that please try out the advise from gregrocker and if that works then you may be saved all the hassle. But even if you succeed you should still complete the project of creating a bootable DVD for the future.
Please tell the what course you have followed. Good luck.
please help i downloaded the img and tried starting a restore but it wont work either