Just ride up and stay on the main road, it winds up through neighborhoods, watch for cars! it will eventually turn into a dirt road, shortly after theres another parking area u could use if you want to start further up away from town. continue up to the top of the pass for great views, then go flying back down! this is a simple dirt road, most people drive up the pass so you have to deal with that, probably not a good idea to go on a holiday weekend! this ride tops out at 11,482 feet, the altitude is the only thing that could make it a diffucult ride as the grade isnt steep or technical. I thought when I did this ride it was ~18 miles out and back starting at the lower parking lot close to main st, so please correct me if you have any more mileage.
from Main st in Breckenridge, Boreas Pass rd is on the south end of town, I think theres a light at the intersection of Main and Boreas Pass rd. go east on Boreas Pass rd, not far you'll see a parking lot on the right, good place to start.
http://www.singletracks.com/item.php?c=1&i=1982