That's the definitely the right way to go especially of you don't really know where they came from. here's the reasons Whychat gives for sending the medical dispute letter and here's the link to the letter. He also suggest you opt out and delete old addresses.
The purpose is threefold.
First, it weeds out any CA that has reported your account without any REAL assignment or authorization from the OC.
Second, it weeds out accounts that were written off, or discounted by the OC and are not valid.
Third, IF the account is verified, it gives you the data you need to pay the OC with the HIPAA letter.
http://whychat.5u.com/http://whychat.5u.com/hipltr.html#DISPUTEQUOTE(Alyssa @ May 5 2006, 01:32 AM)

I am definitely going to try sending a medical dispute letter to fight some of these medical bills that keep piling up. I honestly don't even know where some of them came from... sad I know