Hi Kenny,
We did this route from Uyuni to San Pedro de Atacama a little more than a month ago. We are in a 4wd Toyota. I can give you some info, but out route is not exactly the same as you will be going.

We went into the Salar, then came back to Uyuni to refuel and wash the car. From Uyuni to San Pedro VIA San Cristobal, Villa Alota and Villa Mar was 280 miles. There was no gas after leaving Uyuni. Some say there is gas in San Cristobal, but the 5 travelers we talked to before said there was none.

The road from Uyuni to San Cristobal is good hard packed dirt, some corrugations, but not bad. We turned south at Villa Alota and continued to Villa Mar. This road is worse, some patches of deep sand, but usually alternate routes to avoid getting stuck.

Note that if you do NOT turn south at Villa Alota, and instead continue west to north-south road that goes much closer to the Chile border, the roads will be much worse. And there is a river crossing that is at least 1m deep (as of 2 months ago). This route is longer and a much rougher ride, but there is more lakes and pretty scenic things.

From Villa Mar we cut southwest to the east side of Laguna Colorado. Again some patches of soft sand, but mostly dirt and gravel gravel. Some spots very bumpy. The park entry fee is 150 Bolivianos per person.

In the park things get sketchy. There are lots of roads and routes. Many places of deep sand, and some seriously big bumps and rocks in the road. That said, it is spectacular! From the park exit to San Pedro is 40km of beautiful tarmac.

We did a blog writeup with photos and some more info if you are interested: Bolivia's Southwest Circuit | Life Remotely

Good luck!

__________________
Seattle to Argentina - Starting Oct 2011
www.LifeRemotely.com