My bug report about Norton Internet Security 2004 and this site got eaten by the old host, so I'll repost the part that I remember. The PMs that I sent about it (in the main site) also got eaten.

Anyway, if you try to download a file using IE with Norton enabled it'll sit there downloading the file (with IE claiming to be "getting information about the file"), and then leave you with a 0-byte file with whatever name. Disable Norton, and it prompts for a filename, then downloads the file quite happily except IE doesn't seem to know how big the file is.

As a possible solution, I'd suggest adding to the HTTP response the size of the file (Content-Length header IIRC). I think I have some packet captures of it kicking about, so I can post them if they'd help.