Making a windows boot drive on Mac

So I've downloaded the Windows 7 Ultimate 32 bit OS, and I've tried to make a boot drive using Boot Camp Assistant on my 64 bit Mac. However when I tried to format my 8gb USB, I get this error from Boot Camp Assistant -

Boot Camp only supports 64-bit Windows installation on this platform. Please use a ISO file for 64-bit Windows installation.

Is there anyway I can still make the boot drive on my Mac without having to re-download the Windows OS? Thanks