It indeed is old, at least CUDA 2.1 is required, your card is 1.2: CUDA - Wikipedia
On a multi-core machine not all cores are selected by default. If you want to use all cores (and thus get to 100%, and rather unresponsive machine) you can use RhinoCycles_SetThreads to change the thread count. If you give 0 you should see better CPU utilisation.
/Nathan