When you say "bulk up" do you mean, get larger muscles or toned muscles.  I'm assuming you're meaning toned muscles.  Higher reps and lower weights will do it, but you have to work the entire arm and shoulders. 

Shoulders are key to running as well.  Runners who strength train their shoulders do it to improve their speed.  The faster you're arms move the faster you legs will go and you need strong shoulders to do it.

Building Arms:  Start with curls for your biceps. Find out the maximum you can curl and then do 3 sets of 10 reps with 50% of you max weight.  For example, if you can curl 25lbs one time for your max weight.  Use 12lbs for your 3 sets of 10 reps.  Rest 1 min. between each set.

Next, do the same method for your triceps.  Remember to start with your weaker arm first and do the same with your stronger arm. This is for developing muscle balance, you don't want to have one arm bigger or toner than the other.

Strengthening Shoulders: Thats a little more technical and I'll need to see if I can find a youtube video, it's much easier to learn.

Roy