You could bike it in 4 hours. You will be one hundred percent fine. Cab it (probably 40-ish make sure he takes the A110/100) or take the 109 bus to Zoologischer Garten then to Hauptbahnof and then the Airport express (two changes, boring and annoying) suggest cab.....

I haven't heard if there is a shuttle serving the two airports yet - they may rally and provide some help to people they're making travel difficult for.

a lot of heads are rolling and more will roll. Won't open till 2013 now.