Uploaded Files Empty - Apache configuration problem?

Hi,
I'm in the process of moving an existing website from a shared host to
a dedicated server. The dedicated server is running CentOS 4, Apache
2.0.52 and PHP 4.3.9.

The site is PHP based and a few forms on the site upload files.

The uploaded file is stored in the /tmp directory and then moved to its
final destination by PHP. This is working fine on the shared hosting
account. But on the dedicated server, none of the file data is
uploading. The final stored file has a size of 0.

The $_FILES array in the PHP script that processes the uploaded file
contains the usual information e.g.

array(1) {
["file1"]=> array(5)
{
["name"]=> string(16) "file_name_1.jpg"
["type"]=> string(24) "application/octet-stream"
["tmp_name"]=> string(14) "/tmp/phppaZGQm"
["error"]=> int(0) ["size"]=> int(0)
}
}

But as the last value shows, the size is 0. I'm uploading an 80k jpeg
so there's no problem with max file size limits. All file upload
directives are enabled in the php.ini file.

I can't figure out what could be causing this. My PHP works fine on the
other server so I don't think that's the problem. It must be a
configuration issue somewhere, but I can't figure out where.

Is it an Apache or PHP config issue? A permissions issue? Or maybe
something to do with the OS config?

Apologies if this isn't the right place for this query, but I'm at my
wits end and any help would be greatly appreciated.