Because they are different operating systems?
Surely it is the MB, CPU and hardware in the computer that determines whether an operating system is compatible with it. That is why I asked what difference it should make, especially as Windows 7 64bit successfully runs on that build.
I have attempted 6 downloads and these have had a different SHA1 Hash to that shown on the Microsoft download page. The first one was burned to disk before I realised the SHA1 was incorrect, and it returned an error when tested in VirtualBox. I used Mozilla for three of these downloads after the Internet Explorer downloads returned incorrect SHA1 results. I also heeded the advice of a contributor to the Microsoft forums and tried to download through Free Download Manager but this also returned an incorrect SHA1. These downloads were performed separately on a laptop running Vista 32bit and two different desktop computers, one running XP Pro 32bit and the other running Windows 7 Pro 64bit. It is the Windows 7 computer I am hoping to run the Consumer Preview on. Incidentally, you may have gathered from this that I am downloading the ISO version having already confirmed that my computer has passed the Setup test. No-one can say I haven't tried!!!
Thanks for your suggestions, please keep them rolling in.