The Detroit News ran a special section right around Thanskgiving listing all the tax foreclosures in Wayne county I beleive. You can call up the county and get a listing or a link I'm sure. But like Darlene said, gaining clear title to the home is the more pressing issue. There could be mortgage liens, water bills, or other issues you need to take care of, not to mention the homes may not be livable
If your strategy is to pick up one or several of these homes then your best bet is to consult with a real estate attorney to fill you in on the process. You can also speak with a real estate agent if you wish to look at other sorts of properties.
If you're asking because you saw an infomercial though, don't beleive that there are all these great homes out there for $500, because there aren't. Like the saying goes, you get what you pay for.