wordpress: how to extract array of custom fields on a page

i have a private page that has a series of custom fields. what i’d like to do is be able to discover how many of these fields are filled and then populate a sidebar based on the contents of the fields. i have a block of code that works, but it always looks for those four fields specifically and if there’s nothing in there, it’s just displays an empty block.

here’s the code i’m wanting to condense and make smarter:

    <li class="sponsorSlot">
        <a href="<?php echo get_post_meta(158, 'sponsor_01_uri', true); ?>" title="<?php echo get_post_meta(158, 'sponsor_01_uriTitle', true); ?>">
        <img src="<?php bloginfo('stylesheet_directory'); ?>/<?php echo get_post_meta(158, 'sponsor_01_image', true); ?>">
        </a>
    </li>       
    <li class="sponsorSlot">
        <a href="<?php echo get_post_meta(158, 'sponsor_02_uri', true); ?>" title="<?php echo get_post_meta(158, 'sponsor_02_uriTitle', true); ?>">
        <img src="<?php bloginfo('stylesheet_directory'); ?>/<?php echo get_post_meta(158, 'sponsor_02_image', true); ?>">
        </a>
    </li>       
    <li class="sponsorSlot">
        <a href="<?php echo get_post_meta(158, 'sponsor_03_uri', true); ?>" title="<?php echo get_post_meta(158, 'sponsor_03_uriTitle', true); ?>">
        <img src="<?php bloginfo('stylesheet_directory'); ?>/<?php echo get_post_meta(158, 'sponsor_03_image', true); ?>">
        </a>
    </li>       
    <li class="sponsorSlot">
        <a href="<?php echo get_post_meta(158, 'sponsor_04_uri', true); ?>" title="<?php echo get_post_meta(158, 'sponsor_04_uriTitle', true); ?>">
        <img src="<?php bloginfo('stylesheet_directory'); ?>/<?php echo get_post_meta(158, 'sponsor_04_image', true); ?>">
        </a>
    </li>   

you’ll see what i’m trying to do. it would be nice if it didn’t matter if there were 1 or 8 entries, it would populate what was there without having to explicitly specify. my thoughts were to build an array and then just step through the array to build the elements i need.

thanks all!

WR!