Need help resetting an original MacBook

Model Name: MacBook Model Identifier: MacBook5,1 Software: OSX 10.5.8

How do I factory reset this thing WITHOUT having the OSX installation disc? I've tried booting it while holding command+R and it just boots up normally. What do I have to do differently?

I'd be willing to do some kind of work-around also, like maybe putting the OS on a flash drive would work?

Thanks!