I am an intravenous drug user, am I more susceptible to getting a staphylococcal infection?

Yes. 3 things affect you - one is that you use poor cleaning when injecting thereby pushing the bacteria on your skin into your vein. The second is that the drug may be contaminated with bacteria. The third is that long term IV drug abuse probably affects your immune system making you more susceptible to infections in general.
Yes. Any breaks in the integrity of the skin make one more susceptable to skin infections.