I have never seen a Windows 7 ISO (or real disc for that matter) that contains both 32 and 64-bit versions. Dell doesn't make one (it's one or the other), and Microsoft retail packaging includes each build on a separate disc. I'd be wary.
As for "throwing it on a USB stick", you have to prepare the USB stick and make it bootable before you copy the files to it. Easiest way (IMO) is to use diskpart under Windows 7/Vista.