For SI simulations, HyperLynx uses one core always. Starting in version 8.2 the decoupling analysis will be able to use multiple cores. Using one license, it will use up to 2 (maybe 4, I don't remember for sure) cores. It will be able to use up to (I think) 8 cores by checking out a second license.
If you have HSpice you can take advantage of its multicore support. Go under Setup -> Options -> General menu, click on the Circuit Simulators tab, check HSpice executable and enable the MultiCPU option. Then increase the number of cores to 8. Hope this helps.