It all very much depends on the software you are using. All else being equal, a purely single-threaded application will run better on a higher clocked CPU regardless of the amount of cores it has. However, if you are running a modern OS such as Windows 7 or Snow Leopard that has a multi-core aware scheduler, then more cores could theoretically result in better performance as the OS would assign background tasks to alternate cores while giving your CPU hungry rendering app (almost) exclusive use of its own.
However 3d rendering is a highly parallel and thus easily multi-threaded task, so I would expect modern 3d rendering programs to be multi-core aware in which case more cores would defiantly equal better performance.
As for your video card, the ability for non-gaming applications to offload processing to the GPU is very much in its infancy at this point. AMD and Nvidia have released API's for this purpose. Check if the software you want to use supports CUDA for use with Nvidia GPU's, or DirectCompute for use with any GPU that supports DirectX 11 (such as the Radeon 5000 series or the Nvidia Fermi based series). If the software supports neither then your video card will have no effect on rendering performance.
Also, your 5400rpm hard disk is about the slowest speed you can get for modern drives, I would recommend at least a 7200rpm drive for running your OS and its applications.
But either way your computer should not lock up while rendering, it just might be somewhat laggy during the process. Having 4 cores should help alleviate this issue at least.
