Once you are ready to start you need to make sure that no one can access the existing TFS 2008 server while you do the migration.
You are ready to start
Make sure no-one can check in files by either:
A. Running
TFSQuiesce (recommended)
B. Turning off TFS Service 1. Remote desktop into TFS 2008 2. Start IIS 3. Right click Team Foundation Server | Stop
Figure: You need to stop anyone checking in files
Confirm you can no longer get latest on the team project