Companies are required by law to provide information to employees about their 401(k) plans.

"It's up to you to learn about the plan," says Wendy Rhodes, a partner at Hewitt Associates, employee benefits consultants in Lincolnshire, Ill. "But you can collect a barrel full of stuff to help you if you just take the initiative."

Start with your human resources department. If you don't have one, call the 800 number listed in the 401(k) materials. Here's what to ask: