If 2.0 and 3.0 are installed on the same box, then launching Powershell.exe will start 3.0. To start 2.0, run
powershell -version 2
To quick show if you are runing 2.0 or 3.0, use
To learn more about PowerShell, see our PowerShell 101 Series, or see "Top 10 Active Directory Tasks Solved with PowerShell."