Are you using dial-up? If so, trying using a good download manager that will do CRC checks as it downloads to ensure that nothing gets corrupted. There are several free downloaders available. I forget theirs names but, I used to have similar problems, before getting broadband, and the download managers really helped to clear that problem up. Plus, you can pause a download and continue it later, if necessary. Now I remember, there were two that I used a lot called NetTransport (free version) and GetRight. There are others, though.
Also, what video player are you using? All my videos are tested to run in MPlayer and VLC players.
If necessary, I could split the zip file and you could rejoin them on your end. You would have to install 7zip, if you don’t already have it. I can only offer to do this once, though. I’m curious about what the problem may be. But first, try the download manager and also try to play it in MPlayer or VLC.