big downloading buring

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!