Widgetized Template WP v2.6x vs v2.9x Compatibility

What are some of the potential compatibility issues when upgrading from WP v2.6x to 2.9x, when the widgetized template was designed for WP v2.6x?

The template in question is…

https://www.templatemonster.com/wordpress-themes/21279.html

https://osc3.template-help.com/wordpress_21279/

My guess is that the only thing special about this widgetized template is the navbar at the top of the page. If worse comes to worse, I suppose that I could always hard code the top nav links into place, in the header.php file ???