As a minimum here are something's to try:
FULLY patch it with Windows Update
Install Anti Virus, update and scan (
AVG is good and free)
Install Anti spyware, update and scan (A couple of good removal tools are
Spybot and
Adaware)
Defrag.
Should help with speed, although the machine spec are boardline for XP.
If you do have the discs that came with the system than a reinstall of XP would be the best course of action.
This will completely wipe the system and give you a clean slate to work on.
Quick How-To
Reinstall XP.
This is very simple:
Here's some instructions that should help:
*Look for message "booting from CD" usually located at the bottom of the screen. If you have a factory splash screen, press ESC to unload it.
*Press any Key when you see the prompt to 'Press Any Key"
*Setup will start copying files, if you need to install any third-party or RAID drivers press F6 at this time. The copying of files can take awhile.(leave this one)
*Next you will get the option to repair or enter setup, choose to enter setup. Press ENTER.
*Press F8 if you agree to the license.
*Setup will scan for previous Windows installations
*You want to delete all existing partitions, recreate the ones you want and then install a fresh copy of XP.
Leave to cook for 30-40 minutes
Then install any other Apps you need, like Office, etc.
Hope this helps