I think you're on the right track... here's a test I tried:
<html>
<head>
<title>test</title>
</head>
<body>
<form method="get" action="<?=$PHP_SELF?>">
<input type="checkbox" name="test[]" value="10" />10<br />
<input type="checkbox" name="test[]" value="20" />20<br />
<input type="checkbox" name="test[]" value="30" />30<br />
<input type="submit" name="submit" value="Submit" />
</form>
<p>
<?php
if ($GET['submit']){
print_r($GET);
}
?>
</p>
</body>
</html>
Worked fine for me... $_GET['test'] was an array with all checked values.