Downloaded zip archive incomplete or invalid – can't be unzipped

I just downloaded WordPress 3.0 as a zip archive, but when I try to unzip it I get an error message saying that the archive is invalid or incomplete, and it cannot be unzipped. Anyone else have this problem? I did notice when it downloaded that the download size was 1.5 mb, but it was supposed to be 3.0 mb. Is there a glitch at WordPress when trying to download?