Great answers by Kathy and Jill. Do not limit yourself to foreclosures.
No, you don't need a "special" real estate agent.
A couple of important points: First, don't focus on the tax credit. Sure, it's nice. But find a home at the right price. If you keep focusing on that credit, you may find yourself tempted to overpay. ("Well, it is priced a bit higher, but I am getting a tax credit.") Wrong way to approach the issue. Find a home that works for you and is a good value. Besides, let's say you own the home 8 years from now. Do you think, in 8 years, that you'll have hung onto any of the benefits of the tax credit? If you're smart and frugal--put some into your IRA and some into long-term savings, maybe. But unlikely. And if you buy wrong now, you'll be stuck with your mistake 8 years from now. So: View the tax credit as a nice bonus, but not as the reason to buy now, and not as the reason to buy a specific home now.
Second, to the extent that you might want to take advantage of the tax credit, recognize that you're a lot safer buying from a homeowner--a nice, regular purchase--than a foreclosure. Some banks sell some foreclosures quickly. But others can take a long, long time. (Not as bad as short sales, but still a long time.) If you're worried now about buying before the tax credit expires, imagine how you'll feel about 10 days before it expires and you're still negotiating with the bank.
Hope that helps.