My best advice is to pour yourself into the Wiki, then read through the New Multi-boxers & Support Forum. If you are in a hurry, you can read through these guides to get started, but you'll still have unanswered questions and will need to come back to the Wiki and New Multi-boxers & Support Forum anyhow.

A Plea to all Newcomers
A plea to all newcomers

Vyndree's Guide to Guides
Vyndree's Guide to Guides

Suvega's Brain Dump
http://www.dual-boxing.com/wiki/inde...27s_Brain_Dump

Syro's Multi-boxing Part 1
http://www.dual-boxing.com/wiki/inde...etting_Started

Syro's MB Part 2: How to actually kill stuff
http://www.dual-boxing.com/wiki/index.php/Syro's_Multi-Boxing_Part_2:_How_To_Actually_Kill_Stuff

Wiki Getting Started Page
http://www.dual-boxing.com/wiki/inde...etting_started

If you want to software box (run several windows of wow on a single computer)
Keyclone, a program that sends keystrokes to all your wow windows. It's very easy to set up and configure.
http://solidice.com/

If you want to hardware box (syncronize several computers, each running wow)
PC and Equipment Guide
PC and Equipment Guide for Multi-Boxing.. By Bradster