Well, I'm assuming your a beginner to PHP. This would be like asking a small child to launch a rocket to the moon and back. Can it be done...yes, but I think you should try immersing yourself in PHP and learning about the language before your try something ambitious. Never-the-less, here's some ideas:
You will need to create an engine that spiders the web and indexes words for each website. (This shouldn't be done in PHP, since there is a max execution time on most free accounts of 30 seconds. How about trying C or Java)
You will need a PHP script to search through your keyword database for a query and display relevant results.
It is way more complicated than this. First off, there is enough information on the internet to surpass millions of large hard drives. It is just not feasible to spider the web unless you have access to large server banks. Then you will also need to evaluate each website for reliability and relevance, an algorithm that Google, Yahoo, and others have been perfecting for many years now. In short, this is no small project. Might I suggest trying to create a small version that just spiders your personal website. It's the same principle, just on a much smaller (and more manageable) scale. Good Luck!
Well it looks like the link to images on your index doesn't work. It sets type=Images, but for some reason, with no results. To diagnose this problem, I will need to see your code for index.php. If you don't feel comfortable posting it on the forum, you can PM me. I'll try to do my best at fixing the issue with the different search types.
I will not disclose them here, but I have noticed several extreme security loopholes in your system. If you would like I could also look into these and help you fix them.