This was widely called the "Hummer Exemption" for a while. Do a google search on that to find the exact IRS code. That was part of the reason for the explosion in large SUV sales over the last 2 years.

I thought this only worked for new vehicles? You might want to double check that with your tax person.

EDIT:

I checked today and found this article:

http://www.selfemployedweb.com/suv-tax-deduction-6.htm

It apparently works for used vehicles as well. It is called a Section 179 deduction.

Chuck