1. Ensure that Windows XP uses the NTFS file system.
If you are not sure with yours, here's how to check:
Double-click My Computer icon, right click on C: Drive, then select Properties. Next, check the File System type, see what kind of drive is it. If it says FAT32, then back up any important data. Next, click Start, click Run, type CMD, and then click OK. At the prompt, type "CONVERT C: / FS: NTFS" and press the Enter key. This process may take some time.
NTFS is highly recommended for your PC reliability and efficiency with higher disk drive.
2. Empty the Windows Prefetch folder.
Every three months or more, you empty it very soon, it will be better. Windows XP can "prefetch" portions of data and applications that are frequently used. This makes processes appear to load faster when called by the user. That's cool, but soon, the prefetch folder could be overloaded with references to files and applications which no longer in use. When that happens, Windows XP is wasting time and slowing system performance during loading the file. Nothing is important in this folder, and the entire contents are safe to delete.
3. Once a month, run the disk cleanup.
Here's how: Double-click My Computer icon. Then right-click on drive C: and select 'Properties'. Click the 'Disk Cleanup' button - it only for the right of the Capacity pie graph - and delete all temporary files.
4. Remove all spyware from your computer.
Anti-spyware is needed to perform this.
5. Remove any unnecessary programs.
Use Add/Remove Programs in the Control Panel, don't forget to recheck the directory of the program that just been uninstalled, if there is still any file or folder left, delete it.
6. Scan from viruses
Use Anti-virus to remove all threats.
7. Scan registry
Scan registry with registry scanner, use Registry Cleaner or PC Washer
as the example.
Defragting the computer will help the PC to running faster, because it safe the area inside the harddisk.
9. Clean from dust and dirt
At least once a year, clean your computer of all dust and dirt.