An illegal immigrant can obtain legal status the same way any immigrant can. They have to apply for a Green Card and pass through all of that beauracracy. After seven years of living in the United States, the immigrant is given the choice of applying for USA Citizenship, which allows them to vote and fully partake in everything the country has to offer. They must pass a citezinship test and wait for ANOTHER beauracracy to grade their test. If they pass, they're in!
Make note, however, that illegal immigrants may get in trouble if they reveal they came in unlawfully.
Call the Immigration and Naturalization Service in Washington DC and ask. You do not need to give them your name.