First, you need to be using Tecplot 360 (or the latest version of Focus).
Next, you need to define, in the plt file, the StrandID and the SolutionTime for each zone. These concepts are defined in Chapter 7, section 2 of our user's manual:
For experimenting, it may be useful to use the Strand Editor add-on, which ships with 360 and Focus 2008.
Let me know if you run into any problems.