Custom field data in php statement

For retrieving custom field data, see get_post_meta.
http://codex.wordpress.org/Function_Reference/get_post_meta

Additional functions relating to post meta:
http://codex.wordpress.org/Function_Reference/get_post_custom
http://codex.wordpress.org/Function_Reference/get_post_custom_values
http://codex.wordpress.org/Function_Reference/get_post_custom_keys

Which post do you want to get the meta data from? and what’s the name of the custom field you want data from?

I’d imagine you want something like this then..

<?php
// Get post meta data
$custom_field = get_post_meta( $post->ID , 'flickr_gallery' , true );

// Check if we have data
if( $custom_field ) {

	// We have data, do the thingy
	get_flickrRSS( array( 'set' => $custom_field , 'num_items' => 6 , 'type' => 'set' , 'id' => '30735063@N03' ) );

}
// End if
?>