You should have known when the download completed that you had a bad download. The website states the sizes of the two files:
Download win32_11gR2_database_1of2.zip (1,625,721,289 bytes)
Download win32_11gR2_database_2of2.zip (631,934,821 bytes)
The proper thing to do, when file sizes do not match, is to delete them and try the download again.
Ok. if it's illegal, I'm going to download it again from Oracle.
I used a download manager and I think the file got corrupted because I had to pause the download so many times. Now I hope if the file have errors again, at least I can extract the files I need from the zip.