Magento 1.7 - setting customer group price programmatically

In magento's latest version (1.7) there is an option to set customer group prices, however I can't find any documentation on how to do this programmatically. I tried the following code, but it didn't work. Anyone know how to set customer group price?

    $_product->setCustomerGroupId($_price->getCustomerGroupId());
$_product->setGroupPrice($price);
$_product->save();