We went to the museum a few weeks ago. Don't worry, it's just a few steps as there is a trainstop at Porscheplatz. It's right outside the museum. If you're driving, they have a HUGE parking garage as well. The parking at the OLD museum was pretty bad, but NO PROBLEM AT ALL in the new one.
Be sure to go to the M/B museum AFTER you go to the Porsche museum...After touring both, you'll thank me.