First, I been using Netbeans since Zend Studio merged with Ecplise and let me say i love it. Also, since i met Twig while studying Symfony2 like a year ago i been looking for a decent plugin to highlight my *.twig files without any luck till now.
PHP Twig (that you can download from here) have some little bugs with the validator (like showing 'unexpected block endings', but still works really well.
Besides that this is the first time i had to install an extra plugin for netbeans and i should say it is not intuitive at all. After downloading the *.nbm file i had to google to find out how to install it and the only way to do it is to open the Plugins window --> then Drag the file over it.
I know, there's probably be a better way... i just couldn't find it, so if you know how to do it let me know :)