If you were somehow keeping a connection open and continually sending new data to the browser, you'd see the same problem across most/all the other browsers you've tested (until they time out after 2 or 5 minutes). The script shouldn't care if you're accessing it from NN6, IE, Opera, or Lynx.. It'll just do what it needs to do and exit. So, I'd chalk it up to a Netscape bug. I'll give it a quick test run and update this post when I get to work in an hour...

BUT, $CGI::POST_MAX = 1; ??? You're taking in 'username' and 'password' as params. You probably need a little more than 1 byte to pull these in. Or, am I misunderstanding your usage of this?? You're not passing a username and password through GET, are you?

$CGI::POST_MAX -- If set to a non-negative integer, this variable puts a ceiling on the size of POSTings, in bytes. If CGI.pm detects a POST that is greater than the ceiling, it will immediately exit with an error message. This value will affect both ordinary POSTs and multipart POSTs, meaning that it limits the maximum size of file uploads as well. You should set this to a reasonably high value, such as 1 megabyte.