Most ATMs accept foreign cards. Most large banks change money. Credit and debit cards are now used more widely than before, especially in hotels, shopping malls and upmarket restaurants, but cash remains king in Běijīng, so carry money with you at all times.
Tips are never asked for, or expected. The only time you should ever consider tipping is in top-end luxury hotels or in top-end international restaurants, although they usually tack a 10% to 15% service charge onto the bill anyway. Taxi drivers don't expect tips. Don't be pressured into tipping tour guides – giving them extra on top of their fee is entirely optional.