Corruption generally means you put into the zip files that could potentially run over onto other files inside the zip, (a zip is really just squashed information, and if you have 6000 files all squashed together its highly likely that one or two could leak into others in the extraction process)
Make sure to have backups of any important files before zipping them. If you got this off the net, try searching download.com for it, they generally don't zip or if they do they check for corruption.
Winrar rarely corrupts things, but i don't think it can un-corrupt.
Also, try going back to a previous version of winzip, the older, the slower but less corrupting.