XP might have issues with some games or applications that haven't been updated. The first thing to do is to check with the 3rd party software vendors for any updates to their software to fix any SP2 compatibility issues.
Once that is done.
1. Go to the windows update website and install all critical updates that are PRE SP2. Some of these updates are for issues that can occur after installing SP2. One of those issues is covered here: http://support.microsoft.com/kb/885626
2. Create a System Restore point.
- Click Start > Programs > Accessories > System Tools > System Restore
- select "Create a Restore Point" click NEXT
- type in a restore point description. Something like "Pre SP2 restore point"
- Click the CREATE button. When the restore point is created, click CLOSE.
3. Install and run Ad Aware (with the latest updates) get any spyware off your system.
4. Turn off your anti virus. Right click on your AV icon in the system tray (in the lower right corner) and disable any realtime scanning. This is not always needed but sometimes it helps and it will improve installation performance.
5. Optional: Disable any 3rd party processes running in the background.
- Run MSCONFIG from Start > Run
- Select the Services Tab and put a check mark in the "Hide all Microsoft Services" button.
- Press the Disable All button. Critical MS services will not be bothered.
- Go to the Start Up tab and disable everything.
- reboot for these changes to take effect
6. Make sure you have enough disk space.
7. Download and install SP2. I recommend downloading the entire SP2 package and installing it, rather than using Windows Update. It just takes one more process out of the picture. One less thing that can go wrong.
After the installation and reboot, be sure to go back to MSConfig and re-enable everything. Also re-enable your anti virus realtime scanning...
Note. Microsoft will soon only be releasing critical updates and hotfixes for systems with SP2 already installed. If you do not have SP2 installed, you will not be able to get the updates.