Problem solved. The issue appears to have been that Netscape was downloading the .jar file as a text file. Thus it was corrupted by the download. I got around this by some linux-based trickery. There ought to be some way to get my windows browser to download it correctly. Certainly one easy way would be to distribute the .jar file inside a zip or something similiar, that browsers won't confuse with text files.

Now I'm off to try it out. Cheers!