SP2
means service pack 2.

Windows xp released a service pack, That helped adress a lot of issues with xp.
(SP1)
This wasnt the best theyd ever done so after a while the released SP 2.
After updating there pc's with these service packs Many people suffered problems.
So have been advizing people not to use them.

But Jochi is right.
You should make sure you do have SP2 installed,
It seems to be fine now any way.
Dosent seem to cause errors or CTD's like it used to.

To get SP2
You just need to run windows update.

It's best to update everything you can.

All my xp updates are fully installed,
And theres no problems with them any more.