ISO win 7 - ultimate steal- original product key - complete reinstall?

I have a Windows 7 Pro 32bit ISO that I used to reinstall Windows 7 on my cousin's laptop, he bought his key from the Ultimate Steal and downloaded it through Digital River. I also have Windows 7 Pro 32bit on my laptop from a different ISO purchased through the Ultimate Steal and downloaded through Digital River.

Can I clean install Win 7 on my laptop using my cousin's ISO and my original product key?

I got my original product key using Magical Jelly Bean.

**I plan on using the Windows 7 USB/DVD download tool.

If you have the legitimate Windows 7 Pro 32 bit key, the media from which you install does not matter. You may even download the Windows 7 Pro 32 bit with SP1 from Digital River - in case your previous download was without SP1 and use that ISO

If for some reason Microsoft's USB/DVD download tool is problematic, ( it happened in my case with a Lexar pendrive) , use the Universal USB installer Universal USB Installer – Easy as 1 2 3 | USB Pen Drive Linux to create the bootable pendrive.

You might have to edit or delete the ei.cfg file from the sources folder. If the DVD is coded as Retail and you Product code is OEM (or vise versa) I think it will be rejected. If it is rejected the simple solution is to just delete the ei.cfg file from your thumb drive. That will make your thumb drive a universal install drive. You will get a menu asking which version you want to install, Home, Pro or Ultimate, and it will except an OEM or Retail key. Your product code has to match the version you install so you can't cheat by selecting Ultimate and tying to enter your Pro key.