Off road tri's and Cyclo-Cross bikes

Hey Travis:

As for the XTERRA's, the cross frame "could work", but would set up for some pretty big crashes, or possibly even break the head or steering tube.

At the least, a few hike a bike sections.  The other consideration, depending on how technical it gets(ie Crested Butte or the last Single track section of BEaver Creek) is the amount of pounding it puts on your body leading into the run.

In recent years, the Hard Tail 29er has become a more increasing choice.  After last year, the full suspension 29er is starting to make a good show in both Mountain Bike XC races as well as in the XTERRA's.

As for the roadie to mountain set up and back.  Not just good, but great!

 For the most part, the trails stay pretty wet until about now.  It's bad trail kharma and etiquette to ride on super wet trails as it facilitates trail errosion and such.  Recently, some of the open space areas have been review for shutting down trail access on certain days, to allow access for hikers and horse back, as well as decreasing the errosion.

Point to all that... Most XC and XTERRA racers use the road bike to train through the winter and early spring in order to start the base miles and saddle time.

HEad to Xterraplanet.com for the races here in Colorado.  There are 3 for this year.  A great one to cut your teeth at is XTERRA Indian  Peaks.  Relatively shorter course, and aside from a semi technical short hike a bike, a great intro into XTERRA.

I'd say start with the Roadie, and then build the stable from there.  It's pretty common to have one of each here in Colorado. 

Feel free to call me if yo need some help!