There's some AIM screen names, most notably "powerball4real8," that are being used to scam more deaf out there. Watch also for any with "emerson" in it, like "pacemerson247" that kept getting others. This time it's of someone who is trying to ask you for your password to "open the briefcase" to get the person their money.
First, this is another variation of the Nigerian scam.
Second, this is a gross violation of your account security. Plenty of damage they can do with your account.
Third, it's against the TOS of any service out there to give out your password.
So in short, do NOT give out your password, no matter what. I made this mistake some years ago back in college and had it locked down shortly afterwards. Apparently, someone combined a bunch of files into one huge file and sent it to various people, including the system operators and, unbelievably, the head of operations! Needless to say, I had to do some explaining. I've even broken into a few accounts myself due to weak passwords and my knowing the person well.
Worse stuff can be done with more sensitive accounts. Again, do not give out your passwords. A password like cat-0cargo3 is quite difficult to brute-force crack. The longer your password, the longer it takes.