The process is pretty simple, you can do it over the phone and the fees per credit bureau vary per state, but roughly $30 for all three credit bureaus.
A nice side affect of freezing your credit is that it also prevents you, or someone bad from creating an account to get a copy of your IRS accounts for things like federal tax filing transcripts as I found out when I tried to register for my transcript records.
You will have to "unfreeze" your credit when you want to buy a car or home, and do so about 72 hours prior to requesting credit from someone. The same process applies, call the credit bureau's and unfreeze your account.
Here is the URL's for all three credit bureau's:
FTC credit freeze FAQ: http://www.consumer.ftc.gov/articles/0497-credit-freeze-faqs
Safe retailing ;-)