You won t see any improvement at all if you use Windows 98, since it does not support dual CPUs. You also must run more than one application at a time, or use multi-threaded applications. If you are new to multi-processor systems you may not be familiar with threads. Most users are used to seeing processes. When you run an application, like NotePad, you ll see the process running.
Some applications have multiple smaller executions inside the main process.
These are called threads. For an application to really benefit from a multi-processor system it needs to support multiple threads. The different threads will run on different CPUs and speed up the overall application. A single threaded application will get some benefit from a multi-processor system since it can run on one processor while the operating system runs on another. Again, it depends.