Are you using the Service Providers Directory? You can access it from the "More" tab on your LinkedIn toolbar, then click on Companies. The Service Providers Directory is near the top right hand corner of the Companies page.
This section is a great resource if you are looking for someone like a lawyer, marketing guru, or consultant. This means that you want to be listed here if you are such a person. This happens through recommendations. If someone recommends you and lists you as a service provider, you will show up when your connections search for someone that does what you do!
Notice the tabs near the top of the page: you, 1st, 2nd, world. Use these to narrow down your search criteria. People you have recommended, people your 1st connections have recommended, etc. You can also make a recommendation and request a recommendation from this page. Remember, it is good form to make a recommendation for someone who will be able to return the favor.