Grouping radio buttons

Hi,

I am sitting with a bit of a problem. I am trying to group a set of radio buttons that form part of different entities. Let me give the setup atm:

I have x amount of groups that I list like this:

[Group Name] [Description] [Total Members] [RADIO BUTTON]
[Group Name] [Description] [Total Members] [RADIO BUTTON]
[Group Name] [Description] [Total Members] [RADIO BUTTON]
...
[Group Name] [Description] [Total Members] [RADIO BUTTON]

So now in code I have this:

$form['g_details'] = array(
	'#type' => 'fieldset',
	'#title' => t('Available Groups'),
	'#collapsible' => TRUE,
	'#collapsed' => FALSE,
	'#tree' => TRUE,
	'#theme' => 'group_listing_form',
);

for ($i=0; $i < $group_count; $i++)
{
	$form['g_details'][$i]]['group_name'] = array(
		'#type' => 'markup',
		'#prefix' => '<div>',
		'#value' => '<b>' . $group['name'] . '</b>',
		'#suffix' => '</div>',
	);
	
	$form['g_details'][$i]]['group_description'] = array(
		'#type' => 'markup',
		'#prefix' => '<div>',
		'#value' => '<b>' . $group['description'] . '</b>',
		'#suffix' => '</div>',
	);
	
	$form['g_details'][$i]]['group_amount'] = array(
		'#type' => 'markup',
		'#prefix' => '<div>',
		'#value' => '<b>' . $group['amount'] . '</b>',
		'#suffix' => '</div>',
	);
	
	$form['g_details'][$i]['join_group'] = array(
		'#type' => 'radio',
		'#title' => 'Join this clan',
		'#value' => $i,
	);
}

I get it to display correctly and it's all nicely themed, but when I select a radio and select a different one they are all selected. I need for only 1 to be selected. Anyone know a way to group them?

Thanks in advance.
Davin