ekhm... Actually, bittorrent has data integrity BUILT INTO it. In other words, any file from bittorrent is supposed to be (and not just in theory, every chunk is verified as it downloads) exactly the same file that the uploader has. So if you got a corrupted image from bittorrent, that's probably a rare story.
So ftpdownload+checksum is roughly equivalent to bittorrent..
...
That is not to say wubi throwing a kernel panic is such an unthinkable thing. I don't know how wubi works, but it's a totally new thing, so it might be unstable. Or it might just be that the standard kernel configuration hates your hardware, that happens too at times.
Did you try booting off the livecd? If that *does* work then all fingers pointed at wubi..