http://codex.wordpress.org/Function_Reference/has_term
So…
<?php
if ( has_term('products', 'your_custom_taxonomy', $post ) )
{
get_template_part('products');
}
elseif ( has_term( 'downloads', 'your_custom_taxonomy', $post ) )
{
get_template_part('downloads');
}
?>
Change your_custom_taxonomy
to whatever that taxonomy name is. I changed include to get_template_part
. If this is found in a theme file, that’s the correct function to use. If it’s in a plugin, feel free to change it back.