ABS Troubleshooting

I have a 2000 XTerra with 80k miles. It is a wonderful ride. I have been having problems with my ABS system for a year now. The ABS system no longer works. I am hesistant to take it to a dealer (cost, and I like to do things myself). Has anyone had a similar experience? Do you know where I can find some online help with troubleshooting, diagnosis, or system repair\replace instructions?

Thanks in advance for your help.