We've all had users with the problem in the titel
what can be done
well there are a couple of things that can be done
Check out any obvious problems with the machine
first off have a look in the system tray and the process list to see if anny programs are taking a lot of the system's recources. (the process list can be acessed thru ctrl alt del)
second go thru the installed software and remove anything that the user does not need (notice the distinction between "need" and "use", be careful with this. Some software that the user does use might depend on software that he or she does not use)
Also check how much hard drive space is available. Xp should have at least 500 mb drive space free in order to function optimally
run and install spyware scanners
personally i like the combo of adaware and spybot search & destroy, but to eatch his (or her) own. the reason i like these are a. i've been using them for a long while.
they work really well and complement each other. And to add to tat, both are free.
spybot search & detroy
install and run ccleaner.
ccleaner cleans out the temp files and other crap your computer gathers over the years. it's a great tool for doing a quick cleanup
Clean out the registry errors
CCleaner also has an option to scan for & fix registry errors (on the left, the icon of the brick beeing assembled from smaller bricks .
hav it scan for errors. after the scan is complete there will be a button to fix the errors that are selected. (normally all errors are automaicly selected) press that button.
scan for virussen
With whatever your favourite virusscanner is
I like the widows version of ClamAV http://w32.clamav.net/
and the free version of avg http://free.avg.com/
to scan pc's where there is a virus scanner or you can't install a virus scanner you can use Housecall http://housecall.trendmicro.com/emea/ (an online virus scanner)
defragment the disk
As you move files around on your disk the files end up beeing fragmented on the disk. this can have dramatic impact on the performance on the pc
to correct this open "my computer" right clicking the system drive (generally c:) choosing the "extra" tab and pushing the button defragment. you can than analyse the drive and if needed defragment it.
And if all else fails Reinstall the machine
When you are done reinstalling use clonezilla to take an image of the HD. that way , next time you don't need to reinstall from scratch.