Instant Search has become one of the coolest feature of Google Search, it shows results as you type. You get to the right content much faster than before because you don’t have to finish typing your full search term, or even press “search,” this helping you formulate a better search term by providing instant feedback.
If you wish to integrate a Google like Instant Search to your WordPress Blog then there’s a Plugin for that and its called Wp-Instant. Adding this plugin to your blog is very easy:
Step 1. Download Wp-Instant from WordPress Plugins Directory [Only WP 3.0+ Supported at the moment]
Step 2. Upload it to your /wp-content/plugins/ folder and then activate it from your Plugins page.
Alternatively, you can simply search for “wp-instant” in your Add a Plugin Page and install it. You can then activate it.
The last step is to customize it according to your theme needs. A good tutorial on the plugin’s customize can be found here : Kau-Boys | Customizing the Wp-Instant Plugin