Is it possible to convert a tourist visa into working visa when you arrive in U.S.A. as a tourist?

it's not absolutely impossible, but it's very unlikely. he would have to find an employer not only willing to hire him but also spend the time and money to file a petition for him through USCIS. and he'd still have to be in status on his tourist visa when all the paperwork was approved and ready to go. the skilled worker visa program, is closed at the moment and won't reopen until next April. at that point, the petition can be considered but even if it was approved, he wouldn't be able to work until October 1, 2013. there are some other types of employment based petitions for temporary or seasonal employment, but unless he has some rare skill like sheep herding, and that's a petitionable job that's hard to fill in the US, it's a lot easier to just hire someone already here who can work now.

If he has a B2 visa and he has an employer who is sponsoring him for a work visa. But most likely the timing won't work.

If he is looking for H1B visa, unless he has a cap exempt employer, there are no more visas until next year. There is a limit how many visas of that kind are available each year, and this year they are already used up.

It is very hard to get a visa approved for an unskilled job, so hopefully your friend has at the very least a bachelors degree.