Globals itself isn't really an security issue, it's the fact that poorly coded scripts can be easily exploited with globals on. There is a way to do it, you have to change the form files to get the input a different way.
With globals on, an input field with the name "user" is gotten by the variable $user. With them off, the data in user is gotten with the variable $_POST["user"]. On the join page, variables like $user are used throughout the script. The easiest thing to do is at the top, add the correct way of getting the variables, but then set the other variable equal to it. That way, you don't have to go through the page replacing all instances of $user.
So for the "user" example, at the top of the script under the require("whatever"); you would add $user = $_POST["user"]; This would properly initialize $user without using globals and the rest of the script would work the way it should. The hard part is going through the files and looking for variables that need to be changed. I know for join.php, you should add these:
$submit1 = $_POST["submit1"];
$susername = $_POST["susername"];
$semail = $_POST["semail"];
$submit3 = $_POST["submit3"];
$sfirst_name = $_POST["sfirst_name"];
$slast_name = $_POST["slast_name"];
$sstreet = $_POST["sstreet"];
$scity = $_POST["scity"];
$sstate = $_POST["sstate"];
$szip = $_POST["szip"];
$scountry = $_POST["scountry"];
$stelephone = $_POST["stelephone"];
After that, though, it begins to get a little tough. The problem is for logging in, the sessions also need changed, but you just can't add them to the top of the script because you need them in the proper place in the If/Else statement. You have to check that they used a valid loggin before you set the session. The script is template driven and I converted it to non-globals. I also changed the contact us page to use Sock instead of mail for security and efficiency.
If you want those files, you can have them. I am pretty sure you can just upload them and it won't change the look of you site if you do not overwrite header.php or footer.php.
Another thing, you would need to add this to account.php:
$loggedin = $_SESSION["loggedin"];
$myuid = $_SESSION["myuid"];
$myname = $_SESSION["myname"];