How to open external links in a frame on your site?

I've noticed on some sites, when you click an external link, it stays on the origianl site but opens the website under a frame.. Here's an example: http://www.volunia.com/find/web?q=websites

When you click any external links, you actually stay on the Volunia website, but it opens the other site in a frame under their toolbar thing on top of the screen.

Anyone know how to go about this? Thanks

 

Either fetch the external site w/ PHP or use JavaScript.

 

This site actually has a plugin for it, lol.

 

I found the script they use by digging through their source code. Looks like there's enough code to make your own on this site: http://www.opensearch.org/Specifications/OpenSearch/1.1