I used to use Gaim for my messengers. It will allow you to use several different at the same time and it is free. But I have to agree with most that it can become pretty hairy when you have alot of people requesting support at once. I feel that the easiest way is to use a ticket system and phone supprt as well. I tried several live chat programs and found that most of the people will not use them. One advantage I did like about them was that fact that they had live visitor stats. You could see who was on your site and what page they where actually viewing. It helped me fix some of the other problems that I had and get more conversions. If you do use a live chat type system I did notice that about 99% of the customers would run when you tried to initiate a chat session. I guess they thought it was some sort of popup ad.