Usually i have seen my friends getting frustrated as XP it self is taking up so much space and eating up memory..
What we should do?
See obviously the best way is format the computer and reinstall the OS.. but its hectic and lots of imp data gets lost.

So whats next?
So XP keeps some folders to keep its temporary data!Those ideally should get deleted but they never happen perfectly. So..
Step1: Delete C:WindowsTemp This folder is safe to delete and it again gets created when required by the OS
Step2: Clear c:documents and setingsusernamelocal setingstemp folder.
Step3: Clear the recycle bin.
Step4: Open My Computer and then right click on the installed drive. Select the checkbox for “Compress the drive to save disk space” and let do the job.. it should take some time.
Step5:Uninstall all useless programs or reinstall programs on another drive.
Step6: Clean up your desktop. First it look ugly with lots of icon and 2nd it eats up memory.
Once these are done lets see what if anything else is wrong!
Step7:Click ctrl+altr+del and you get your task manager.
See the Applications running. Stop all the applications present there. And now wait for 5 mins. Now click on the performance tab and see the CPU usage.. A normal flow when you dont do anything should be 0~10 anything more than that means something wrong!
If anything wrong check step8
Step8: Click on the processes tab. You will see lots of application running. Lets figure out whats wrong. Click twice on the CPU tab will sort the thing and give you the applications taking lots of energy. Try to figure out what can be killed.. Reading there description you can come to know. What you should not delete are “explorer.exe” or “Dllhost.exe” and some others. Its best to read there description and folder location and think it can be deleted or not.
Anyways if you kill something and do a mess just restart and it will be fine!

Also defragmenting your hard disk is a good practice!

I think that preety much should help.. From my experience one more thing i can tell.. never ever use cracked antivirus or you are gone.. use AVG Free edition best.
Also do scan your computer with some anti spyware! Use trial version of this: http://www.pctools.com/spyware-doctor/

Hope this post will help!

SoftwareDeveloper, iot, CreativeTechnologist, MobileDev. Love building stuffs