You could try repairing the zip file. I don't have winzip, but I think it has that ability. I use winrar and it is able to repair damaged .rar archives IF the repair bits have been written into the file. Your only other option is to download it again.

I don't think xolox is making the problem as I too have also downloaded WinXP Pro Build 2600, ( That's the one you want.) and it worked just fine. It's likely that someone out there is sharing a messed up file. This is common for very large .zip files. I highly suggest people use the .rar archive format with the repair bits set for very large archives. WinRAR is the best out there IMHO.

Better yet, download the Windows XP Pro 2600.ISO file, it isn't zipped or rarred.