Have you tried the basic Custom Fields that Wordpress includes automatically? If you don't see it at the bottom of your Post edit screen, click the Screen Options button at the top-right of your editor window and check the box next to Custom Fields to make it visible. Once you can see it at the bottom of the editor, click Add Custom Field and enter something like 'event_start' in the Name input, and your start date in the Value field. Repeat that step to create an 'event_end' field. When you create a new post, these fields will be available to you in the Select dropdown under Name.
To expose the start date in your page the visitor sees, use this in your template:
<?php echo get_post_meta($post->ID, 'event_start', true); ?>.