If you are thinking of Full Migration (with History) from VSS to TFS 2010, you must have a plan. Depending on your user security isolations, departments having different needs, dealing with different product lines, two teams interested to adopt different methodology/process template (like MSF Agile document 5.0 vs MSF CMMI document 5.0) and other concerning factor.
The idea starts planning for "Team Project Collections" TPCs. Ideally there should be one TPC in an organization unless two different departments have different target users with different access matrices. Then comes "Team Project" TP. Different Product lines (like Visual Studio vs Office) should have different TPs because each will have different set of target users with specific access needs. Teams with conceptually isolated projects should be in separate TPs because both will have different iterations, milestones, artefacts and people involved. Single TP will have single Check-out, check-in lock, Check-in policy. If two teams have different requirements of policy like one wants "Allow Multiple Users to check-out" and other team not allows this then both should be separated. Here is a basic level presentation on TFS2010 available for download.