1. Make sure you are sending the ENCTYPE as "multipart/form-data" in your form
2. Make sure you are using CGI.pm to receive it.
3. It's not unreasonable to check if it works differently with IE vs. Netscape, and what version you are using. The cgi.pm docs say that inconsistencies arise with different combinations of platform/webserver/browser.

I had the exact same problem with a MacOS9/WebSTAR system, so I looked at CGI.pm more closely. The docs say that the problem could be in the creation of the temp file, which CGI.pm creates with your upload, then transfers it to your specified destination. In my case, I was able to determine that a temp file was being created, but still only 0 bytes .But I was sure that the file was being uploaded by (transferred to) the webserver, just not saved at all. Some said the OS was unable to transfer large files, but my best guess had to do with the CGI glue from the webserver program to perl...