<% if package.screenshots.length>0 %>
<%= link_to (image_tag package.screenshots.first.image_url('small')),
package.screenshots.first.image_url('large') %>
<%= package.name %>
<%= package.description %>
<% else %>
<%= link_to (image_tag "/thumbnail-404.png"),
"/path/to/upload/package" %>
<%= package.name %>
<%= package.description %>
<% end %>