One site I would recommend for info on ADHD is www.chadd.org
Both ADHD and BPD can involve impulsivity but for somewhat different reasons. ADHD impulsiveness is linked more to acting before thinking and some impulsive behaviors are a form of stimulation for a bored ADDer.
Those with BPD become involved in self-destructive
impulsive behaviors such as drug use, gambling, reckless driving, compulsive shopping, etc. to deal with the pain and dysphoria so they will feel better.
Approximately 50% of those with BPD have comorbid ADHD as well. And a substantial percentage of adults with ADHD have BPD (there have only been a few studies but the percentages were 29% to 38%).