Jim: GorgeMedic provided a better answer than what I can write in the "First Aid - When Help is Delayed" thread concerning good samaritan laws.

IRT not knowing what you are doing, this is why you should go dust off (or buy a new) Boy Scout Handbook and go practice some more, or go seek some training.

Considering the dead guy you found by the trail... if there are obvious signs that he is dead (rigor, lividity, etc) then don't start. Once you start, the rule of thumb in the CPR courses I've taken say to go until you are exhausted or relieved.

Aimless: I figure that after about an hour or so (maybe less- I'm older than I was when I worked EMS) I'd be exhausted, and that meets the criteria for stopping in my last CPR class.

Steadman