Finding the RIDs in your domain video
Here is a video I shot a while back that demonstrates how to use ADSI Edit to find the number of RIDs remaining in your domain. However, you can do this more quickly by running the following command: dcdiag /test:ridmanager /v | find /i "available RID"
How to find the RIDs left in your domain
Technorati Tags: Active Directory Domain Services RIDs