Force DC out of AD

Hello,

I have a test network of approx 4 machines. These machines were configured as W2K DCs in order to test various items. When testing was completed, certain machines were released to perform other tasks.

The problem is that the DCs were never demoted, so that the remaining DC with AD still contains the listings for these servers. Being that they are DCs, I cannot simply delete them. I have attempted to change the primary group, and I cannot simple format this last DC.

Therefore, the question is: How does one force out DCs in AD when the listing is no longer valid?