Big Downloading and Buring Problem

I downloaded Vista Beta 2 32-bit version with their download manager, and it
took an eternity, but the end file is only 12kb...

So I downloaded it again, useing Firefox's download manager, and this file
came as only 179Mb.....

I don't get it.

when I try and burn it with Nero it gives me the following error:

The entering block size does not correspond to the image length. The block
size may be wrong. Do you want to correct the value or ignore the problem?

correcting brings me to a screen where I can set the type of image, the
block size, image header size, trailer size, and if it's scrambled or
swapped. ignoreing continues to the destination drive and burn speed select
window, however it comes up as cd-r/rw and it's a dvd image. It won't let me
burn it to a dvd-r.

Help!