you're trying to access a script on another server that is running the script. therefore the other server is possibly using the variable for instance it's evaluating it on it's end, but not passing it to you.
server A:
requests a page on server B:
http://www.somedomain.com/show_variable.php?displayvariable=5
server B: runs request to display variable #5 and outputs
qwerty
server A: receives variable, and stores it or does whatever because the output would be in the variable
for instance
$stealpassword = readfile('http://www.somedomain.com/password.php?revealpass=admin');
server A:
echo $stealpassword;
code on server B: would have to interpret revealpass switch/variable and have register globals set to ON.
also it would have to know what to do when revealpass was set, such as echo admin's password?
that's just a scenario that came to mind when you mentioned what you're wanting to do, if i'm wrong try to be more descriptive of what you're wanting to do, and we'll see what we can tell you.
clandestine