Off-Setting Travel Through Carbon Credits

I'll be going "home" this week, to Kansas City for a writer's and editors conference. We have a gas guzzling 4WD truck, and while I'm concerned about the cost of gas, I'm more concerned about the impact we have on the environment. In our defense, we do need 4WD here, there's days we wouldn't make it off this mountain without it, and when we bought this truck in 2005, 4WD hybrids where very new and overly expensive and difficult to get.
Right now, the best I can do is try to offset my travel by investigating carbon offset companies, doing the calculations of how many emissions I'm contributing and purchase some credits.
These credits are then used to invest in clean energy. For a list of the most efficient carbon credit companies, I'll be looking at:
http://www.cleanair-coolplanet.org/ConsumersGuidetoCarbonOffsets.pdf
and making an informed decision when I return from KC.
Due to my trip, Going Green will be taking Wednesday off. I'll be back online with more "green" stories about my trip to Little Rock - and maybe Kansas City - next week.