I started running when I decided to start Crossracing. But the running in the race isn't like slow-endurance running, it's more like short bursts and sprint intervals. The exception is when some sections might be faster to run than to ride, depending on your bike handling skills.

In fact, the entire race is like sprint intervals on drugs, both running and on the bike. 10 seconds on, 3 seconds off, 40 seconds on, 5 seconds off, etc. The overall-intensity is cranked up to 11 the entire time. If you can handle red-lining your heart rate for 30+ minutes, you're good to go.

Used/decent cross bikes will run you around $1200 from what I've seen. Mountain bikes can absolutely be used (and I have done this depending on terrain), and is a great way to try the race before making heavy investments. Be aware that you gotta carry that sucker up some steep run-ups, and you will become very aware of every pound very quickly!

-- gnat! (Go for it! It's fun! Honest!)