If you are running Creo Ansys, there is a configuration option, put in your "config.pro" file to specify the number of cores. From the list of options:
creo_ansys_solver_cores <number>
"Set the number of processor cores to be used by Creo Ansys solver. Currently Supports 1-4 cores."
Default value is 2.
Apparently, if you're using Creo 9.0, this setting is available in the user interface, as discussed here:
UI Setting of Cores for Ansys Simulations
If you're running Creo Simulate (not Ansys) I don't know how many cores it uses, but I see there is a config.pro option for Creo 9.0
sim_run_num_threads <number>
This option will "Specify the number of CPUs that Creo Simulate Native mode will use for running the analysis. The possible values are: ALL (default), ALL_BUT_1, ALL_BUT_2, 2, 1, HALF. "
