problem with fwrite function

I can't write to files on my serveur using the fwrite function. I verified
all write access-rights to the directories and there is no problem.
When using ftp I can place files on my serveur (no problem by this way).
I don't have any problem to access files with " fgets " reading stuff from
files on my providers sever.

Here the example program I used :
<?
$test_str = "test"
$send_file = "http://www.my-serveur-name/test.htm";
$file1 = fopen("$send_file", 'w');
fwrite($file1, "test_str");
fclose($file1);
?>

What is the problem?
The function ftp-connect and the other " ftp_..." functions aren't
unfortunately supportet so that I have to exclude this way to copy files on
my server!

Thanks for your remarks and helping.

Didi