Check out my getting there and route description on this page:http://www.summitpost.org/from-spruce-grove/697859#
It will help you find the footbridge. It's a little odd as you have to weave through the campground to get there.
Grab Trails Illustrated map #105 if you haven' already - it will have all you need for this area. If it's too late to order it online, many gas stations / convenience stores / even grocery stores along the Hwy 285 corridor should carry it.
And, yes, you can get to the Lizard Rock trail from SG CG: http://www.fs.usda.gov/recarea/psicc/re ... 7&actid=34