<?php
$cat_id = 8; // set desired category id
$category = Mage::getModel('catalog/category')->load($cat_id);
$products = $category->getProductCollection()->
addCategoryFilter($category)->addAttributeToSelect('*');
?>
<?php foreach ( $products as $_product ): ?>
<a href="<?php echo $_product->getProductUrl() ?>">
<img src="<?php echo $this->helper('catalog/image')->
init($_product, 'small_image')->resize(135, 135); ?>"
width="135" height="135" title="<?php echo $_product->getName() ?>"
alt="<?php echo $_product->getName() ?>" /></a>
<?php endforeach; ?>