There are some differences in the interviewing process of small companies vs. large companies. Here are a few things to be prepared for.
Though "selling yourself" is still the goal whether you're applying at a small company or a large company, sometimes what you need to emphasize about yourself is different.
Many times in a small company, for example, you may interview with the top dog (the company's founder). This is a person who has a really personal stake in the success of the company, as it represents a substantial investment - in time and money - for him or her.
In a case like that, that person wants to see the same type of enthusiasm and passion from you. Be ware that you may also have to talk to several other people in the company from different departments. In smaller companies separate departments work closely so "fitting in" will be a major consideration here.
In smaller companies, you may not be offered any kind of training. It's important to exhibit in the interview that you are able to work without direct supervision, and that you're flexible and are willing to perform any task.
When it's your turn to ask questions, try to steer things toward company goals. You might be able to get an idea of the company's viability and potential for growth from the responses you get.
Lastly, be prepared to negotiate salary. Since this is not a company that's been around forever and has established pay rates for certain positions, you have some wiggle room.
Now, with a large company, your first meeting will more than likely be with someone from HR. This person will be armed with standard, generic questions that are used to hit on the high points of your experience and to see if you drop all the keywords they're looking for (e.g., network administration, project management, Windows 7, etc.) You may even be asked to take a test to measure your technical skills.
I know many of our readers are frustrated by the HR part of the interview but if you're prepared and knowledgeable of what the position requires, then you should do OK.