I am a boxer looking to improve my speed, power, explossiveness & endurance will i achieve this by weight lifting in the 8-12 & 20-25 rep range?

Yes and no..: 8-12 reps for max effort will give you power. 20-25 reps with sets will give you endurance. To gain speed and explosiveness, you need to do hand work that encompasses that action. Train for the technique, vary your workout. Doing the same thing over and over will cause your body to "acclimate" to your action and stop improving. Keep your routine varied, high intensity interval training.