Hide/Show Fieldset based on radio button selection

I am working for a client integrating authorize.net with ECHECK capabilities and in my form have a radio button that selects whether the customer wants to do a transaction with a credit card or direct debit.

The problem is, I have both fieldsets showing all the time, and I would like to only show the fieldset for the credit card entry when that is chosen and only the fieldset for direct debit when ECHECK is chosen.

I am not really sure how to move forward on this, whether AHAH can / should handle this or if I should embed JQUERY into the form element.

If anyone can point me in the right direction that would be wonderful.

$montharray = array('01','02','03','04','05','06','07','08','09','10','11','12');
	$yeararray = array('09','10','11','12','13','14','15','16','17','18','19','20');

	$form['amount'] = array(
		'#title' => t('Amount to load'),
		'#type' => 'textfield',
		'#size' => 6,
		'#weight' => -2,
		);
	$form['customer_info'] = array(
		'#type' => 'fieldset',
		'#title' => t('Billing Info'),
		'#weight' => 0,
		);
	$form['customer_info']['first_name'] = array(
		'#title' => t('Your First Name'),
		'#type' => 'textfield',
		'#description' => t('Please enter your first name.'),
		);
	$form['customer_info']['last_name'] = array(
		'#title' => t('Your Last Name'),
		'#type' => 'textfield',
		'#description' => t('Please enter your last name.'),
		);
	$form['customer_info']['address'] = array(
		'#title' => t('Address'),
		'#type' => 'textfield',
		'#description' => t('Please enter the billing address'),
		);
	$form['customer_info']['city'] = array(
		'#title' => t('City'),
		'#type' => 'textfield',
		'#description' => t('Please enter the city.'),
		);
	$form['customer_info']['state'] = array(
		'#title' => t('State'),
		'#type' => 'select',
		'#options' => array(
								'AL'=>"Alabama",
                'AK'=>"Alaska", 
                'AZ'=>"Arizona", 
                'AR'=>"Arkansas", 
                'CA'=>"California", 
                'CO'=>"Colorado", 
                'CT'=>"Connecticut", 
                'DE'=>"Delaware", 
                'DC'=>"District Of Columbia", 
                'FL'=>"Florida", 
                'GA'=>"Georgia", 
                'HI'=>"Hawaii", 
                'ID'=>"Idaho", 
                'IL'=>"Illinois", 
                'IN'=>"Indiana", 
                'IA'=>"Iowa", 
                'KS'=>"Kansas", 
                'KY'=>"Kentucky", 
                'LA'=>"Louisiana", 
                'ME'=>"Maine", 
                'MD'=>"Maryland", 
                'MA'=>"Massachusetts", 
                'MI'=>"Michigan", 
                'MN'=>"Minnesota", 
                'MS'=>"Mississippi", 
                'MO'=>"Missouri", 
                'MT'=>"Montana",
                'NE'=>"Nebraska",
                'NV'=>"Nevada",
                'NH'=>"New Hampshire",
                'NJ'=>"New Jersey",
                'NM'=>"New Mexico",
                'NY'=>"New York",
                'NC'=>"North Carolina",
                'ND'=>"North Dakota",
                'OH'=>"Ohio", 
                'OK'=>"Oklahoma", 
                'OR'=>"Oregon", 
                'PA'=>"Pennsylvania", 
                'RI'=>"Rhode Island", 
                'SC'=>"South Carolina", 
                'SD'=>"South Dakota",
                'TN'=>"Tennessee", 
                'TX'=>"Texas", 
                'UT'=>"Utah", 
                'VT'=>"Vermont", 
                'VA'=>"Virginia", 
                'WA'=>"Washington", 
                'WV'=>"West Virginia", 
                'WI'=>"Wisconsin", 
                'WY'=>"Wyoming"),
		'#description' => t('Please select your state'),
		);
	$form['customer_info']['zip'] = array(
		'#title' => t('Zipcode'),
		'#type' => 'textfield',
		'#description' => t('Please enter the zipcode'),
		);
	
		$form['transaction_type'] = array(
		'#title' => t('What payment type would you like to use?'),
		'#type' => 'radios',
		'#options' => array(
							'ECHECK' => "Direct Debit",
							'AUTH_CAPTURE' => "Credit Card",
							),
		'#weight' => 1,
		);
	
	$form['card_info'] = array(
		'#title' => t('Card Info'),
		'#type' => 'fieldset',
		'#weight' => 2,
	);
	$form['card_info']['card_number'] = array(
		'#title' => t('Card Number'),
		'#type' => 'textfield',
		'#default_value' => '4111111111111111',
		);
	$form['card_info']['exp_month'] = array(
		'#description' => t('Month'),
		'#type' => 'select',
		'#options' => 	$montharray,
		);
	$form['card_info']['exp_year'] = array(
		'#description' => t('Year'),
		'#type' => 'select',
		'#options' => $yeararray,
		'#default_value' => '15',
		);
	
	$form['bank_info'] = array(
		'#title' => 'Bank Info',
		'#type' => 'fieldset',
		'#weight' => 3,
		);
	$form['bank_info']['name_on_account'] = array(
		'#title' => "Name associated with account",
		'#type' => 'textfield',
		);
	$form['bank_info']['account_type'] = array(
		'#title' => "Type of account",
		'#type' => 'select',
		'#options' => array(
						'CHECKING' => "Checking",
						'BUSINESSCHECKING' => "Business Checking",
						'SAVINGS' => "Savings",
						),
		);
		
	$form['bank_info']['routing'] = array(
		'#title' => "Aba Routing Number",
		'#type' => 'textfield',
		'#size' => 9,
		'#maxlength' => 9,
		);
	$form['bank_info']['account_number'] = array(
		'#title' => "Account Number",
		'#type' => 'textfield',
		'#size' => 20,
		'#maxlenght' => 20,
		);
	$form['bank_info']['bank_name'] = array(
		'#title' => "Bank Name",
		'#type' => 'textfield',
		);
	
	$form['submit'] = array(
		'#type' => 'submit',
		'#value' => t('Submit'),
		'#weight' => 10,
		);

	return $form;