Joomla! Forum - community, help and support

Hello all, I am new to Joomla and have just installed a template from template monster. Aside from my homepage, all my URLs contain index.php after the root. I have tried switching 'Search Engine Friendly URLs' to Yes. That 404s every page apart from the homepage. Another forum post suggests the problem is with the htaccess file. The one supplied with the joomla template causes a 500 server error so I have had to rename this htacces_1 just to get the site to load. All advice and tips would be massively appreciated. I have a virtual beer here for anyone who can help!
Many thanks all... Andy