I'm trying to help out a guy I know.

He came from Mexico about 10 years ago, if I had to guess I would think he came over illegally. Anyhow as far as I know he's stayed out of trouble the whole time he's been here. My brother wants to hire him, but doesn't want to until he can obtain a green card.

Can someone obtain a green card easily if they entered the country illegally?

If so what steps does it take, and what's the average amount of time it can take.

I think he has never tried to do it before, because of fear of being deported.

First, he is not qualified for work visas if he entered US without inspection or overstayed the visa.

Second, he may become legal if he marries a US citizen but this is not an easy path. He will have to file a waiver and get an approval in order to adjust his status, plus he will have hard time proving that it's not a sham marriage.

Since 9/11 there are many changes in immigration laws and it's not easy anymore.