This FAQ is... a lot more detailed than I expected. Actually a pretty interesting read even if you don't care about tax protestors per se. Digs into everything from history of federal taxation powers to how individual laws are codified into the United States Code.

My favorite of the particularly frivolous arguments: the IRS code refers to "taxpayers", and if you refuse to pay tax, you are literally not a tax payer, and therefore the code doesn't apply to you.