Another thing is Start/Run and run msconfig. This calls the System Configuration Utility, on the far right of which is a tab called Startup. Have a look at what is being loaded at startup, uncheck any you don't need. If you're not sure, it *probably* won't do any harm unchecking, but in many cases you will be able to discern what is obvious crud.
Also, try to become a little familiar with the Task Manager - right-click on the taskbar, Task Manager, open the Processes tab. You'll get a very busy screen of what is actually running at that moment. You won't do any harm by flicking on the top tabs (CPU, Mem Usage, etc) to reorganise the display. If anything is hogging the box, you'll be able to find out here, and short of killing off processes you won't do any damage.