Give Provide Support a try. The system looks professional (this is what our clients say), but at the same time it is very easy to setup and customize. It shouldn't take more than half an hour to have live chat up and running on your client's website. We offer a fully functional trial, so you will be able to test all our features directly on the website or using the Live Demo tool in your account.
If you need any assistance with setup, send me a private message. I will be glad to help you with any questions, including technical ones. You can also contact our technical support that is available through our support chat 24/7.