If your friend has a million dollars, he may be in luck. The law requires most people to invest that much to qualify as immigrant entrepreneurs.

There are, however, some variations on the million dollar theme. The initial investment can be as little as $500,000 if the business is in a depressed locale. On the other hand, the immigration authorities can require the investment to be as much as $3 million if it's in a ritzy place.

To qualify as an immigrant entrepreneur, your friend would also have to take an active role in the business, and the business would need to employ at least ten full-time workers. (Meeting these standards can be difficult, leading to the denial of many investors' green card applications.)

There are other, more general immigration requirements to meet as well. For example, green card applicants must have a record scot-free of serious criminal convictions and must make it through various medical and security checks.

If it sounds as if your friend might qualify, consider it a wise business investment to pay an experienced immigration attorney to process the application or to recommend alternate strategies. Legal advice is definitely in order if your friend is currently living in the United States without documents.