If I've understood you correctly, you want Google to crawl your "category" directory, but not the single page within it called internetmarketing.php.
In that case, all you need in your robots.txt file is:
It will continue to crawl every other page in "category", (provided it can access them, of course).
If you want to block all search engines, and not just Google, then use:
Remember, this will only stop well-behaved bots whih respect the robots.txt file; it won't protet you from bad bots.