IRS assistance is 'advertised' as being available to help you prepare your IRS Form W-7.
If like the majority of the other people on this planet you haven't found the instructions worth their salt the IRS advises that you call 1-800-829-1040.
BAHOOT! As my old instructor would belch. Today...
A new online tool has been created by the IRS for taxpayers with international tax filing requirements that is worth checking out. Here are some relevant links:
Advance Pricing Agreement (APA)
Advance Pricing and Mutual Agreement Program (APMA)
Alien, Departure Permit