Will that php word on a vbulletin page or will it need a variable ?
Yeah, you need to use a variable. If it's a global then {vb:raw GLOBALS.usernameErr} might work (although it's kind of cheating), otherwise you need to register it to the template.
Quote:
I'm using the get method because on the post method it redirects me with this:
I'm not sure what's doing that, but you could try adding this in your form:
You *could* use GET, but everything will be on the url, and you'd need to check $_GET instead of $_POST. You can check $_REQUEST to get either one, but it's probably better to use the one that your form is using unless you have a reason to do otherwise. (Sorry if you already know all that - you probably know more than I do when it comes to non-vbulletin php).