I like the Gallery Formatter module for my galleries. It's the Colorbox module is nicely integrated with galler formatter to give you a cool lightbox popup. Gallery Formatter will use the first image in your multi-value CCK image field as the first slide image, so you can drag the order of the images in the node form into the order you want them to appear in.
If you want to display the first image of your multi-value CCK image field separate from your gallery (like in a view that gives a preview of each gallery), I would first create an ImageCache setting that you want to use to display that image, and then output that image in your node template like so:
<?php print theme( 'imagecache', '[your_image_cache_preset_name]', $node->field_gallery_images[0]['filepath'] );?>