Decrease Visual Effects 
Turn off some of the "visual effects" to get a faster computer
- Click Start on your taskbar
- Select Control Panel
- Click to Open "System"
An alternate method is to right click
My Computer on your desktop and select Properties. (A third way is to hold down the Windows key and press the pause/break button.)
The System Properties dialog box will appear.
- Select the Advanced tab
- Under Performance section click the Settings button
the Performance Options dialog box will appear
Remove the check beside the following options:
- Fade or slide menus into view
- Fade or slide ToolTips into view
- Fade out menu items after clicking
- Show Shadows after menus
- Slide open combo boxes
- Slide taskbar buttons
- Use a background image for each folder type
- Use common tasks in folders
Increase Virtual Memory 
- Right Click on My Computer -> Properties -> Advanced Tab
- Under Performance Click Settings -> Advanced
- Virtual Memory -> Change
- Select Custom Size set your minimum and maximum as high as possible according to your Hard Drive's Free space, (Like 1024-2048)
Temporary Files 
Note: This is for advanced users only.
- Go to your Windows XP directory. (e.g: C:\WINDOWS)
- Go to the C:\WINDOWS\prefetch\ folder and delete everything there. Restart Windows and your computer will be faster.
- Go to C:\Documents and Settings\CurrentUsername\Local Settings\temp\ and delete everything there, where CurrentUsername is your username. (Hidden files must be viewable.)
- Go to C:\WINDOWS\temp and delete everything there.
- Search for *.tmp and *.chk and delete those.