3. The Easiest Option: Buy, Don't Build
Linux has now matured enough that there are now system integrators who will assemble a workstation for you, install and configure a Linux, and do an intensive burn-in to test it before it's shipped to you. If you have more money than time, or you have stringent reliability or performance requirements, these integrators provide a valuable service by making sure you won't get hardware that's flaky or dies two days out of the box.
For those of us without a champagne budget, the rest of this HOWTO is about how to install Linux yourself.