If you want to physically prepare for cross, there are several elements to incorporate into your training. But first, make sure to get clearance from your doc.

Most cross racers begin running in June or July each season. Start very slow with short runs (5 minutes to begin) and work up to about 60 minutes total. Once you have a running base, you can add speedwork into your training. All courses are different, but most running is either up or down hill, so running on a trail will simulate the requirements of an actual race.

In addition, you'll want to learn the basic skills (mounting, dismounting, carrying the bike). In many regions you'll find clinics in August and September. Attend a clinic or ask an experienced racer to show you the skills then practice them. Eventually, you'll want to practice your skills at speed within the context or a higher-intensity ride. I recommend spending one day each week when you just focus on skills. You can make some barriers and set up a simulated course. And have some fun with it.

If there isn't a clinic near you, Adam Hodges-Meyerson from Cycle-Smart.com has a good skills DVD. There was also a series of skills videos on VeloNews.com lat season -- you could probably still find them online.

It's also fun (and educational) to watch cross DVDs -- there are a bunch out there!

For riding, you'll want to keep your aerobic base, so include one longer ride each week (2+ hours). However, you'll also want to incorporate some HIT intervals.

Hope this helps!