My laptop is very slow

Follow above suggestions all are good ones, and also apply the following suggestions:

1. Disable startup programs as follows:
Go to Start \ Run \ type "msconfig" (no quotes) and press Enter... in the Startup tab, uncheck all programs except for the antivirus and any you may need to start with Windows, press Apply and next click on the Sevices tab, check the box where it says: Hide all Microsoft Services, and uncheck all but the Antivirus process, to disable them... Press Apply and OK.

2. Delete Temp files that may accumulate in the thousands if you never delete them, and cause slow and erratic system behaviour:
Go to Start \ Run \ and type: %Temp%, press Enter and Delete all files contained in the folder that opens. Next again in the Run command, type Temp and press Enter and also delete all files.
To configure Temp file auto deletion, read how to with a Group Policy (Gpedit.msc) edition.
http://windowsstart.blogspot.mx/2008/06/auto-delete-temporary-folder.html

3. Scan the System with a fully updated Antivirus and again with Malwarebytes Anti-Malware.

4. In My Computer, go to your System drive Properties C:\right click\Properties\Tools tab\and click on Defragment Now\Defragment...

5. Run the Windows Disk Checker application to verify for bad disk sectors and correct file system errors:
Start \ Run \ type; CMD and press Enter... next type CHKDSK C: /R . A message will appear stating that the volume is in use and prompting you to schedule the disk check for the next startup, press Y and follow with Enter. The system drive will be checked during the next start.

6. Install Glary Utilities or Tune Up Utilities to clean the registry and delete system junk so your Windows runs a bit better... most of the times noticeably faster and stable. CCleaner also does some good cleanup but Tune Up Utilities is much more efficient, and Glary Utilities is a free similar to Tune Up Utilities which can be used for up to a month for free with all the functions enabled. Next install Services Tweak 2.0 to disable unnecessary Windows Services. http://www.insofter.com/app/1193972/services_tweak.html It can re-enable services to defaults with a single click.

7. If you use the Sleep Mode regularly, make a habit of temporarily disabling Hibernation on a regular basis: Find Hibernation in the Control Panel \ Power Options \ Hibernate. This feature causes problems because the Hiberfil.sys file (C:\Hiberfil.sys) saves the Stand-by and Sleep Mode/Hibernation information, and tends to corrupt after a while of continuous use... this causes long startups, no startups, and when working normally even causes system freezes, frozen mouse pointer, lags and slowness. This is so common that in my case it causes some or most of these problems almost everytime I use the XP Hibernation, so I usually keep Hibernation disabled and only enable it when I really need to put the system in Hibernation.

8. Occasionally delete the Prefetch files in C:\Windows\Prefetch folder. Prefetch files are supposed to help applications load faster during startup but at the expense of slower system startups.. Prefetch files also tend to accumulate over time and should be regularly deleted because like temp files, only the most recent prefetch files are usefull. I may be oversimplifying this part (click links & read about it) but it's safe doing it, 1st based on the amount of articles about it on the web, and 2nd because I occasionally delete these files w/o a problem. I use Unlocker to delete them as they can't be deleted directly via mouse context menu. But you can disable the Windows Prefetcher from saving unused prefetch files which tend to accumulate over time and just like Temp files bloat your system making it run slower. Read how to here:

How to Disable the Prefetcher Component in Windows XP
http://support.microsoft.com/kb/307498

9. Lower Hardware Acceleration: Configuring this setting helps if the computer repeatedly freezes momentarily a fraction of a second to several seconds before resuming normal activity. Right click on your Desktop > Properties > Settings > Advanced > Troubleshoot > Slide the Hardware Acceleration control to the left a notch and click Apply, OK, and OK, and observe if the computer improves, and repeat if necessary.

10. Run the System file Checker: To replace corrupted or missing System Files which can be damaged or deleted by viruses, malware, user errors, disk errors, application uninstallations, electric cut-offs, etc. Insert the installation CD or DVD in the CD/DVD drive and type "SFC /SCANNOW" (no quotes) in a Command Prompt Window and the Sysem File Checker will replace or install System files that may need to be refreshed.

Most of the times and unless the computer has major problems, these tweaks should make any computer speed up to or close to it's normal speed for the installed hardware resources, apply these tweaks and watch the difference... how big a difference may depend on how bad the problem; So expect only a return to normal speed for the installed hardware and their condition.

Prefetcher
http://en.wikipedia.org/wiki/Prefetcher

Gaining Speed: Empty Prefetch on your Windows XP System
http://www.windowsnetworking.com/articles-tutorials/windows-xp/Gaining-Speed-Empty-Prefetch-XP.htmlhttp://en.wikipedia.org/wiki/Prefetcher

Tweak Prefetcher for faster Windows startups
http://lifehacker.com/201453/tweak-windows-prefetch-for-a-faster-startup