That's a big no-no. Gambling with another person's money is a great way to lose that person's trust and friendship.
I'll second that as much i love gambling it's with my own never with any one else money, simple reason one I can't be answerable to anyone, plus one can't be at mercy of others. I would like to have that friend in my life, money comes and goes but friend are always. I think people should not do this, as it will destroy their credibility in the other persons eye.