CGI timeout problem

hello,

I wrote a very simple upload script and it perfectly works for small files. But if the file is too huge (I tried with 8Mbytes), my browser displays:
"
The page cannot be displayed
....
Cannot find server or DNS Error
Internet Explorer
"

instead of uploading the file and submitting the form to my "upload.php" file. I set my upload_max_size to 10MB both in php.ini and in my form. And my web server is running under IIS 5.

here is one of my user feedback:
"
CGI Timeout

The specified CGI application exceeded the allowed time for processing.
The server has deleted the process.
"

does it mean that I have to use set_time_limit so the script doesn't time out ? I don't really understand why I should do that.

thanks,