Can one of you Wordpress Gurus give me some help please?

I developed a Wordpress site on:

http://domain.com/renewables.

It was a stand-alone version of Wordpress and now the site is nearing completion, I have moved it to its own domain.

It now resides at:

http://newdomain.com

I changed the DB settings in wp-config and all was fine. The homepage was on the correct URL and all other pages were still pointing to the development URL, so I employed the URL fix thus:

From: http://codex.wordpress.org/Changing_The_Site_URL

Edit theme functions.php
update_option('siteurl','http://newdomain.com');
update_option('home','http://newdomain.com');

Now only the homepage works and the links throw up a 500 error.

Any idea on how best to make this move work?

There used to be a find and replace plug-in for the DB, but I can't find that any more.