Having a problem where the form submits before the validateUsername function has a chance to complete the username check on the server-side.

How do I submit the form only after the validateUsername function completes? Hope this is clear...

form.submit(function(){
	if (validateUsername() & validateEmail() & validatePassword()) {
		return true;
	} else {
		return false;
	}
});			

function validateUsername(){			
	usernameInfo.addClass("sign_up_drill");
	usernameInfo.text("checking...");
	var b = username.val();
	var filter = /^[a-zA-Z0-9_]+$/;		
	$.post("../username_check.php",{su_username:username.val()},function(data) {
		if (data=='yes') {
			username.addClass("error");
			usernameInfo.text("sorry, that one's taken");
			usernameInfo.addClass("error");
			return false;			
		} else if (!filter.test(b)) {
			username.addClass("error");
			usernameInfo.text("no funny characters please");
			usernameInfo.addClass("error");
			return false;	
		} else {
			username.removeClass("error");
			usernameInfo.text("ok");
			usernameInfo.removeClass("error");		
			return true;	
		}
	});				
}