It's not hard to make a P2P download system that checks the file to make sure it's accurate. Take a look at eDonkey and BitTorrent for more evidence of that. Both, to my knowledge, check for anything corrupt in the download as they download the file. I know for certain BT does this and I'm fairly certain eDonkey does as well (at the very least I've never downloaded a corrupted file). Either way, BT is proof positive that P2P can ensure a perfect download.
[edited by jab1981 on 24.02.2005 13:51]