At first, I though it was a bit harsh but the more I think about it, your response was appropriate. I'm a younger guy (20) and one job I have is as a personal protection agent. Oftentimes in school or elsewhere, I'll meet a girl and in our conversation I'll list off what I'm doing now and since that job is one of them, I sometimes get a scary admission from them: "Really? Umm, I ahhh, have a problem with this guy/girl..." Needless to say, I have gained some experience with defeating stalkers, and one of the most helpful things is severing the channels in which they interact with you. Now, you're not being stalked (as far as I know), but since AIM is all about communication, here's what your options were:
1. Block him. I like this one, but there are ways around it. Someone can create another screen name and add you to the buddy list to see if you're on. If they switch back to their original SN and see you offline, they know what's up. By then, hopefully, they would've gotten the message.
2. Ignore his messages. Who wants to put up with that annoying crap, though?
3. Do what you did (tell him NO). In a real case of stalking, the first step in promoting legal action is for the stalked/stalkee (word?) is to make a clear and definite request for the stalker to back off. "I don't want you hanging around me", etc, done seriously. In your case, the "I don't want to talk to you" should be clear enough. If someone doesn't understand that they are really goddamn stupid.
As a guy, though, I do have to ask why you gave him your contact info if you didn't want to talk to him? That's just asking for trouble. If Newegg.com sold problems, your order payed the employees' year-end bonuses. Be aware of what messages your feigned interest sends. You've heard the guys complain in this thread about "leading us/him on." Girls are too often confused with what they want (until they get older) and that confusion messes with our heads. For guys, the gray area is far more painful than either the black or the white. Here's a classic: "I like you

)) as a friend

()."

+

=

. Left without a conclusion, we're either going to proceed forward or pull away until we get one. You gave this guy one

. If you feel bad about it, don't. His life, like yours, will go on.