With sample page :
<form enctype="multipart/form-data" action="<?php echo $PHP_SELF; ?>" method="post">
        <input type="hidden" name="MAX_FILE_SIZE" value="100000">
        Send this file: <input name="userfile" type="file"><BR>
        <input type="submit" value="Send File">
</form></CENTER>
<HR>
<?php
        echo "Field : " . $userfile ."<BR>";
        echo "File : " . $_FILES[userfile][name] ."<BR>";
        echo "Type : " . $_FILES[userfile][type] ."<BR>";
        echo "Temp : " . $_FILES[userfile][tmp_name] ."<BR>";
        echo "Size : " . $_FILES[userfile][size] ."<BR>";
        if (is_uploaded_file($_FILES[userfile][tmp_name]))
                echo "Download : Ok<BR>";
        else    echo "Download : KO<BR>";
        }

On RedHat 7.2 (PHP 4.1.1, Apache 1.3.23) no problem,
$userfile=none or path to /tmp/xxxxx

On HP-UX 11i (PHP 4.0.6, Apache 1.3.19 build by HP) no problem.

On HP-UX 11i (PHP 4.1.1, Apache 1.3.23 build from source) $userfile and other variables are empty.
(It's work one time on many)
Compile flags :

./configure  --with-oci8  --with-apache=../apache_1.3.23
--with-gd=/opt/gd --with-pdflib=/opt/pdflib
--with-jpeg-dir=/opt/jpeg-6 --with-png-dir=/opt/libpng
--with-tiff-dir=/opt/tiff-3.5 --with-zlib-dir=/opt/zlib
--enable-sigchild --with-mysql=/opt/mysql
--enable-sockets --with-tsrm-pthreads

Thank's for your help.