What  it comes in the mind while running any operating system. why it is slow : while many applications are running on your computer and now the provider of the  Windows XP  and window vista   are also giving tips and tricks to speed up the computer.

wehave already given tips for botup and shutdown as how to speed up your Windows xp Boot Up and Shutdown

By using the   tools  provided in the window XP  service  pack3  and vista  you can  maintain your computer very efficiently. This tools   safeguard   your computer  from  the undesirable functions and privacy too.

Speed up your computer with the  following 5 modes :

1. Free up disk space
By freeing disk space, you can improve the performance of your computer. The Disk Cleanup tool helps you free up space on your hard disk.
2. Speed up access to data
Disk fragmentation slows the overall performance of your system. When files are fragmented, the computer must search the hard disk when the file is opened to piece it back together.
3. Detect and repair disk errors
In addition to running Disk Cleanup and Disk Defragmenter to optimize the performance of your computer, you can check the integrity of the files stored on your hard disk by running the Error Checking utility.

4. Protect your computer  against spyware
Spyware collects personal information without letting you know and without asking for permission.
5. Learn all about  ready boost

If you’re using Windows Vista, you can use Ready Boost to speed up your system. A new concept in adding memory to a system, it allows you to use non-volatile flash memory—like a USB flash drive or a memory card—to improve performance without having to add additional memory.

For more emphasized and step by step details read more on Microsoft.com which is the source of this post.