A+: Task Manager as Diagnostic

Windows Vista/XP/2000 can display the Windows Task Manager when you press Ctrl+Alt+Del (select Task Manager from the Windows Security dialog box).  Windows Task Manager in XP has tabs for Applications, Processes, Performance, Networking and Users. The top-level menu can be used to adjust the properties of the currently selected tab and to shut down the system.
Use the Applications tab to determine if a program has stopped responding; you can shut down these programs. Use the Processes tab to see which processes are consuming the most memory. Use this dialog along with the System Configuration Utility (MSConfig) to help determine if you are loading unnecessary startup applications; MSConfig can disable them to free up memory. If you are unable to shut down a program with the Applications tab, you can also shut down its processes with the Processes tab, but this is not recommended unless the program cannot be shut down in any other way.
Use the Performance tab to determine if you need to install more RAM memory or need to increase your paging file size. Use the Networking tab to monitor the performance of your network.