Very sorry for the delay. The size you report is roughly what I see. My computer shows it's a 353K file, but minor differences like that happen depending on the filesystem.
I'm not sure why it won't unzip, but my best suggestion is to try and re-download the file. We have many users downloading and installing JLinked every day, so I don't think it's an issue with the file itself.
Beyond that, can you tell me if you're using the built-in zip tools with Windows, or a 3rd party program like WinZIP or WinRAR?
I'm not sure what's happening, but somewhere along the path to your computer, it seems to be getting corrupted. If you're using a download manager or some other tool to get the file, that could be causing a problem as well.
I really don't have many better suggestions than to try downloading from another browser, at least, or a whole other computer to see if the same problem occurs? I couldn't tell if your test on WinXP was with the same file you originally downloaded, or if you attempted to re-download it again, so maybe you already tried that. Again, we have many downloads of that file every day, so the file is definitely valid that's published. We just need to narrow down what's different in your case.