Here's a must read booklet from WiserWomen.org:

Divorce And Retirement: How To Take Control Of Retirement Benefits

One of the most important terms to understand is the Qualified Domestic Relations Order "QDRO"

Get a “Qualified Domestic
Relations Order” (QRDO)

If you plan to ask for a share of your husband’s retirement benefits, you need a qualified domestic relations order or QDRO.  (Orders for retirement plans of government employees may have different names.)

The QDRO is a court order that is usually written by one of the couple’s attorneys. It orders the retirement plan to pay you a specified share of the benefits based on the terms of your divorce agreement. Your lawyer will submit the QDRO to the court for a judge’s signature. After the judge signs the QDRO, send it to the plan administrator as soon as possible.

Your agreement should specify whether you or your husband is responsible for preparing the QDRO and paying the related fees.

What happens if you don’t get
a QDRO?

You could end up like
thousands of women who reach
retirement age only to find out that
they won’t get what the divorce
decree stated because the
documentation wasn’t handled
properly.