What replaced DSA.MSC in Windows Server 2008?
dsa.msc still very much exists in 2008 and 2008 R2. It gets installed automatically on machines that have the Active Directory Domain Services role installed. For machines that aren't running the AD DS role, you just have to install it.
- Open Server Manager, go to the Features section
- Add Features
- Remote Server Administration Tools - Role Administration Tools - Active Directory Domain Services Tools - Active Directory Domain Controller Tools
- Next, Finish, etc
You can also get the snap-ins for non-Server OSes with RSAT (Remote Server Administration Tools).
An elaboration on Ryan's answer, due to Telos' feedback.
- Server Manager
- Features
- Add Feature
- Remote Server Administration Tools
- AD DS and AD LDS Tools
- AD DS Tools
- AD DS Snap-Ins and Command-Line Tools
The description for this entry says it includes Active Directory Users and Computer, Active Directory Domains and Trusts, Active Directory Sites and Services, and other tools.
Once added, I was immediately able to go to start -> run -> dsa.msc, and it launched, with no reboot needed.