Wordpress built-in export (WordPress eXtended RSS or WXR) would contain your posts, pages, comments, custom fields, categories, and tags. Images can be donloaded from the old location (must be live) to the new one; be sure to check the "Download and import file attachments" box on import.
If there are galleries managed/created by some plugin then you'd have to have a more detailed look at the particular plugin used.